Rocks and Fossils

Public summary: 

Find out about explosive volcanoes, shiny crystals, and the exotic animals that lived millions of years ago.

A box of rocks and fossils
Useful information
Kit List: 

In this box there should be:
• DK fossil book
• DK rocks and minerals book
• viewer (a magnifying glass on a stand)
• Box 1 - Clear plastic box with the main rocks and minerals collection in
• Box 2 - Orange plastic box with rocks, minerals, gem stones and fossils in
• Small box of plant fossils
• Laminated visual aids including some activity sheets

Packing Away: 

This kit should be packed flat in the box so it doesn't rattle around.

Frequency of use: 

If you’re confident with demonstrating and know your geology give this kit a go though, and please write down the bits that work and don’t work. (A sheet of paper that stays in the box would be great!)

Most of this kit was bought by a biologist (Lia) who claims to know nothing about geology, so if there’s more kit that would be useful please let us know!

***The explanation below is out of date but is kept as it has useful information about the specimens - skip to the bottom for a list of specimens and their places in the boxes (see the attached pictures for how to put it back) as well as some suggested activities that could be carried out with the samples. ***

This demonstration consists of a large number of different rocks and fossils, which may seem a little bewildering at first. Don’t worry, I’ve studied Geology for three years and I still don’t know much about some of the specimens we have. If you’ve done 1A Geology/Earth Sciences or something similar, you should know enough to demonstrate a decent number of the rocks and fossils. If you need help on specific specimens, there is a list of contents with each set, I’ve prepared this guide to hopefully give additional explanation, and there are books on fossils and minerals in the box too.

I like letting the children hold the rocks and fossils, and look at them under the magnifying glass, as I feel it makes things a lot more interactive. This is fine; just make sure they’re careful with them, as the fossils in particular are quite fragile. It might be best not to let the smallest children handle them, for the sake of the fossils and the children’s windpipes.

There are a few ways to go about this demonstration, which you can vary depending on the venue you’re demonstrating in, and what suits you best. You could keep the boxes closed and only bring out specimens one or a few at a time which you want to talk about, or you could leave out all or lots of them, and let the children lead the demonstration a little more. I find the second option more interesting, and it tends to draw children in more easily in a public event, but I might keep most of the specimens in their boxes at a school, especially if the children want to just grab everything in sight! However you choose to do demonstrate, you don’t have to talk about anything you’re not confident about. You can either leave specimens in their boxes, or admit you don’t know much about them if children ask.

One thing I find interesting about this experiment is the variety of opinions about geology. Some children will think rocks are really boring, while others will love fossils or crystals, and want to talk to you all day! It can be really rewarding convincing people that rocks and fossils are interesting, or talking to a child who is fascinated by everything you say, but if sometimes you’ll talk to kids who really don’t want to know. I usually try showing them the bits I think they’ll find most interesting, but in the end I might just send them to another experiment if they’re clearly not getting anything from this demonstration.

You can use the specimens as links to talk about almost anything you (or the children) want. A lot of them come from the Atlas Mountains in Morocco, so I might use this to talk about continental drift and mountain-building, as they were formed by the collision of Africa with Europe. I often end up talking about the rock cycle and how fossils are formed and preserved (or not). I also like talking about the structure of the Earth, and why it’s hotter underground. The visual aids are there to help you with this sort of thing, especially if like me you end up rambling about something completely unrelated with a group of intelligent and interested children! If there’s anything else you feel would be useful to include, by all means mention it to a committee member, write it in the tour diary, or even print it yourself - this experiment is still relatively young, so any input would be appreciated.

I should perhaps include a warning that you may occasionally have to deal with people, who do not believe in evolution, think crystals have healing powers, or something similar! Unfortunately it’s unlikely you’ll manage to persuade them against these beliefs, but you could have a go!

The rest of this guide provides brief details about each specimen, and some ideas about what to talk about with each one, but remember, this guide is in no way complete, and there are probably interesting things I have left out or simply don’t know about plenty of the specimens. We’ve included the box of plant fossils in this experiment box, which is written up as part of the plant experiment (biology). There are some notes to go with this, but you’ll probably only want to use these if you’ve studied plants at some point. It’s fine to just leave them in the box and use the rest of the kit.

All specimens should be labelled.

The Fossils Box:
At some point it is a good idea to ask children if they know what fossils are and how they form. If they aren’t too sure, explain how hard parts of animals – teeth, bones, shells – can be buried under layers of sediments, and eventually become fossilised. However, plants, footprints, tree sap and excrement can all be fossilised too. The fossil we see may be as it originally was, it may have recrystallised, or it may be an imprint. The details of fossilisation processes are actually very complicated, but fortunately a general idea of what happens is sufficient. The book in the box explains this for a general audience, so it's probably worth a look through.

Wikipedia says that:
"Fossils (from Latin fossus, literally "having been dug up") are the preserved remains or traces of animals (also known as zoolites), plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous (fossil-containing) rock formations and sedimentary layers (strata) is known as the fossil record. The study of fossils across geological time, how they were formed, and the evolutionary relationships between taxa (phylogeny) are some of the most important functions of the science of paleontology. Such a preserved specimen is called a "fossil" if it is older than some minimum age, most often the arbitrary date of 10,000 years ago.

Hence, fossils range in age from the youngest at the start of the Holocene Epoch to the oldest from the Archean Eon several billion years old. The observations that certain fossils were associated with certain rock strata led early geologists to recognize a geological timescale in the 19th century. The development of radiometric dating techniques in the early 20th century allowed geologists to determine the numerical or "absolute" age of the various strata and thereby the included fossils.

Like extant organisms, fossils vary in size from microscopic, such as single bacterial cells only one micrometer in diameter, to gigantic, such as dinosaurs and trees many meters long and weighing many tons. A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Preservation of soft tissues is rare in the fossil record. Fossils may also consist of the marks left behind by the organism while it was alive, such as the footprint or feces (coprolites) of a reptile. These types of fossil are called trace fossils (or ichnofossils), as opposed to body fossils. Finally, past life leaves some markers that cannot be seen but can be detected in the form of biochemical signals; these are known as chemofossils or biomarkers."

An awkward question I have been asked a few times is how do we know that a given fossil is 50 million years old? This is a hard one to answer, since most of the fossils are old enough to be dated using Uranium decay series. If children are old enough to understand Carbon-dating, you can make an analogy with this, otherwise you may have to make do with talking about relative dating using layers of sedimentary rocks.
The timeline should be useful for talking about ages of various fossils, since large numbers of years become a bit meaningless, but saying that something lived twice as long ago as the first dinosaurs impresses most children.

 Bivalve
These molluscs have lived in a huge variety of situations. They can be marine or freshwater, live in deep or shallow water, above or buried in the seabed, or even swim like scallops or attach themselves to rocks along the coast like mussels (both kinds of bivalve) do. Their shell consists of two usually symmetrical halves called valves, but some bivalves, such as Gryphaea (or Devil’s toenails) have one valve much bigger than the other. They have been around since the Cambrian.

 Amber
Amber is fossilised tree resin (not sap apparently, although I’m not entirely sure what the difference is). Animal and plant material is often preserved in amber, particularly insects which have become stuck in the resin. As far as I know, this is the only way in which insects can be preserved, as their exoskeletons are simply too weak to be fossilised normally. Children may have seen Jurassic Park, in which the DNA of a dinosaur is extracted from blood that a mosquito has drunk before becoming trapped in resin and fossilised. This idea has some basis in fact, since the preservation of fossils in amber is so good that fragments of DNA may be recovered. Unfortunately, unless we’ve found a new piece of amber, there are no insects in this one.

 Gastropod
Gastropods are another group of animals which have lived in various different situations. They can be freshwater, marine, or even live on land (e.g. the snail), and have been around since the Cambrian. They can be recognised by their coiled shell. I often just use the words “sea snail” here, since I’m not sure the word “gastropod” will add much, but it’s up to you.

 Shark Teeth
The box contains a variety of shark’s teeth. These are some of the most easily recognisable fossils we have. There is an opportunity here to talk about why sharks have such sharp, and often serrated, teeth, as well as why they are such common fossils (sharks have many sets of teeth and frequently lose and replace them). Sharks have skeletons made from cartilage, which makes them unlikely to be preserved, and have been around for more than 420 million years. One of the teeth is from a shark related to the Megalodon, which some children may have heard of. It lived roughly 28 to 1.5 million years ago, could grow up to around 20 metres in length, and had huge impressive jaws!

 Brachiopod
These shelled organisms used to be far more common, occupying many of the marine environments which bivalves do today. Their shells are made from two halves, or valves, which tend to be different, and can be distinguished by a mirror plane down the centre of each valve. They have been around since the Cambrian, and were most common during the Paleozoic.

 Ammonite
These marine molluscs had spiral shells and were alive during the Mesozoic- the same time as the dinosaurs. These should not be confused with Nautilus, an animal with a spiral shell more closely related to the straight Nautiloids. They can be told apart by the position of the siphuncle – a tube used to move water between the shell’s chambers and control buoyancy – which runs along the outer edge of ammonites’ (and all ammonoids’) chambers, but through the centre of Nautiloids’. Ammonites vary in size from a couple centimetres to a couple metres, and are commonly found on the Dorset and Yorkshire coastlines.

 Goniatite
These are another type of ammonoid (the subclass to which ammonites belong) which rarely exceeded 15cm in diameter. They can be told from ammonites by their simpler suture line (the line where the divisions between chambers make contact with the edge of the shell) and lived earlier than ammonites – during the late Paleozoic.

 Trilobite
These are an extinct class of arthropods which lived during the Paleozoic, though they declined towards the end of it. Trilobites were some of the first animals to evolve hard parts (which is why they are also some of the earliest fossils that are regularly well-preserved) and eyes. Their hard shell meant that they could roll into a ball to protect themselves (as I think this specimen is doing). Their eyes were made from calcite crystals which had to be orientated correctly to avoid a double-image (you can demonstrate the double-image with the calcite crystal in the minerals box). Some had their eyes on stalks, while others were blind. Most moved over the sea-bed, but some swam, and they could be predators, suspension feeders or scavengers. The name trilobite refers to their three “lobes” – one that resembles a spine down the middle of the trilobite, and one on each side of it. I usually liken trilobites to woodlice to help children to imagine them.

 Triceratops Bone
Whole fossilised bones, and especially whole skeletons, from land-dwelling animals are pretty rare, as they will only be buried and fossilised in an area where deposition is taking place, such as the sea or a delta; much of the land is being eroded. If the animal does not die in a place where its bones are quickly buried, the bones may be separated from each other, bashed around, or even fragmented before finally being buried. This is probably what happened to this piece of triceratops bone. The small holes are most likely where the marrow used to be.
Triceratops was an herbivorous dinosaur with three horns on its head (two above its eyes and one on its nose), a large bony frill, and a beak-like mouth. It walked on four legs and grew up to 9 metres long and 3 metres high. It belongs to a suborder of dinosaurs called ceratopsians, which had similar features, but different numbers of horns. There is discussion as to whether the horns were primarily for defence against large predators such as Tyrannosaurus Rex, or for fighting amongst each other for mates. Triceratops lived at the very end of the Cretaceous, which provides an opportunity to talk about the mass extinction at the end of this period which wiped out the dinosaurs (one of several that have been identified throughout the Earth’s history). A lot of children will know the most popular theory- that the Earth’s collision with a huge meteorite caused the extinction. Far fewer may know about the less popular hypothesis, that an enormous set of volcanic eruptions covering half of India in lava flows known as the Deccan Traps in less than a million years contributed to this extinction event, or may even have been the primary cause. Both of these events happened, but there is debate as to which was the main cause of the mass extinction.

 Mammoth Bone
This fragment of woolly mammoth bone has much bigger holes in it than the Triceratops bone. This implies that it had a lot bone marrow, which led a scientist I was talking to to suggest that it might be from a femur (thigh bone). Most children will have seen Ice Age, so describing woolly mammoths as “Manny the big hairy elephant from Ice Age” seems to work quite well. These animals lived from roughly 150,000 years ago until 10,000 years ago, although a race of dwarfed mammoths continued to live on Wrangel Island (about 200km north of Siberia, just inside the Arctic Circle) until about 4000 years ago. There is debate as to what led to the extinction of mammoths and other large ice age mammals such as sabre-tooth tigers and giant beavers around 10,000 years ago. The main hypotheses are hunting from humans and climate change; although in reality it may have been a combination of the two.

 Mosasaurus Tooth
From the canine-like shape of the tooth, we can tell that this is from a carnivorous animal. Mosasaurus was a huge sea-reptile that reached 15-20 metres in length (I like to compare this something real, like the length of the room I’m in). It was alive during the late Cretaceous, and was another victim of the mass extinction at the end of this period.

 Echinoid/Sea Urchins
The sea urchin is a member of a class of animals called echinoids. Echinoids are related to star-fish and tend to have a similar five-fold symmetry, though this may be less obvious depending on the specimen. During life, sea urchins are colourful balls of spikes that live on the sea-bed, feed mainly on algae, and can be found shallowly enough in warm seas such as the Caribbean that people occasionally step on their spines (which can hurt a lot!). The spines are designed to protect sea urchins against predators. They fall out within several days of the animal dying, leaving fossil sea urchins with tiny holes where each of their spines were attached during life.

 Coral
Coral have been around since the Cambrian, but the kind we know today (called Scleractinian coral) such as this fossil only evolved during the Triassic when the old Rugose and Tabulate corals became extinct. Corals (with the exception of some Rugose corals) are colonial organisms which form huge coral reefs. These can be hard to explain to children; I find it helps if they’ve seen Finding Nemo. I like to use coral to talk about continental drift, as I have found fossil coral in the Lake District- clearly not the warm shallow sea favoured by these organisms.

 Turtle Shell
The oldest known turtles lived during the Triassic. The fossils we have are individual plates (or scutes), many of which together would have made a whole turtle shell. There is an opportunity here to talk about the usefulness of having a huge shell you can hide inside.

 Straight Nautiloid
Nautiloids have been around in one form or another since the late Cambrian, and are today represented by the spiral-shaped Nautilus (mentioned in Ammonite). Straight Nautiloids are often cut and polished to be sold by crystal-sellers. The animals that lived inside these shells were squid-like, but from a different sub-class to squids.

 Crinoid/Sea Lily
Sea lilies are crinoids which are attached to the sea bed by a stalk. Crinoids have lived since the Ordovician, and, despite their name and plant-like appearance, are actually animals. They use their arms to trap small particles of food.

The Minerals Box:
Or, more accurately, the minerals, gemstones and other stuff box.
The colours of many minerals such as quartz and calcite are determined by the presence of impurities, particularly transition metals. Whether they dissolve or precipitate in a particular setting depends on the solubility of the mineral in groundwater, which depends on a number of things, including temperature and pressure. The growth of crystals in this way can be likened to the growth of salt/sugar crystals in a bowl of salty/sugary water left out to evaporate, except that it is changes in temperature/pressure etc that mean that the water is over-saturated and a mineral will precipitate rather than the evaporation of water. This is how geodes (balls of crystals) of amethyst, quartz etc can form in water-filled cavities deep underground.
The most impressive crystals I have heard of are the 12m long crystals of gypsum (which is softer than fingernails) in the Cave of Crystals in Mexico, which is essentially a giant geode.

See book for more detailed notes than those I have included.

Wikipedia says that:
"A mineral is a naturally occurring solid chemical substance that is formed through biogeochemical processes and that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not have a specific chemical composition. Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms. The study of minerals is called mineralogy."

• Pyrite
Pyrite is also known as Fool’s Gold due to its similarity in physical appearance to gold. It is found in quartz veins, coal beds, sedimentary and metamorphic rocks, as well as a replacement mineral in some fossils. It is associated with other oxides and sulphides, and often forms during diagenesis- low pressure and temperature alteration to deposited sediments during early compaction which may result in recrystallisation and precipitation of minerals. Its chemical formula is FeS2.

• Calcite
Calcite is a form of Calcium Carbonate, and is one of the two main minerals from which animal shells (as well as Trilobite eyes) are made. It is rare to see such well-formed calcite rhombohedra as the one in the box. Calcite is strongly birefringent, which means that it has different refractive indices for light oscillating in different directions. This means that light entering a calcite crystal splits up into two beams polarised in the directions of the highest and lowest refractive indices, causing a double-image if you look through it. Limestone is mostly made up of calcite, and this can recrystallise during metamorphism, or calcite can form stalactites and stalagmites in limestone caves. It often cements together other sediments if it has precipitated from the water trapped between individual grains of sediment, forms veins particularly in fractures in rocks, and can be found in some mantle-derived rocks. It is harder than fingernails but softer than steel (Mohs hardness of 3), and is colourless and transparent with no impurities. I find a lot of children assume that calcite and quartz are the same thing because they are both clear- this is an opportunity to talk about other ways of telling different minerals apart such as crystal shape, hardness and birefringence.

• Red Aragonite
Aragonite is the other main form of Calcium Carbonate from which animal shells are made. It is metastable and will revert back to calcite over 10s to 100s of millions of years and means that aragonite fossils are often replaced by calcite. It is often found in sedimentary rocks and cave deposits. The red colour is probably due to impurities such as iron.

• Connemara Marble
Marble (not a mineral but still lives in this box) is a rock formed by the metamorphism of limestone and other carbonate rocks. However, Connemara Marble, which comes from the region of Ireland of that name, is not technically a marble. It is a serpentinite breccia. Ultramafic rocks are close to the composition of the mantle, are brought up from the mantle in magma, and tend to contain a lot of a mineral called olivine. Heat and the presence of water can metamorphose olivine into another mineral, serpentine, transforming the rock into serpentinite. A rock made from broken up pieces of serpentinite is a serpentinite breccia, such as this Connemara marble (see Breccia). The main other minerals in this rock are carbonates. The green colour is common in ultramafic rocks, probably due to nickel and reduced iron.

• Quartz
Pure quartz is SiO2. It is very hard (Mohs hardness of 7) - harder than steel – which is why most sand is made up predominantly of quartz, as softer minerals wear away more quickly when battered by waves on the coast or the winds of the desert. Quartz is the main ingredient of window glass, usually in the form of sand. It can be formed in a variety of ways, including as a metamorphic or igneous mineral, a cave deposit, or as quartz veins in fractures in rocks. It can crystallise in fluid-filled cracks and holes underground to form geodes – balls of quartz crystals. Pure quartz is clear and colourless, but often quartz has impurities which change its colour, and can make rose quartz (pink), smoky quartz (grey) and other varieties. Quartz is piezoelectric, which means that it distorts when a voltage is applied across it, and can generate its own voltage when the applied voltage is removed as it returns to its original shape. This sets up a circuit with a frequency determined by the resonant frequency of the quartz crystal, and is used to keep time accurately in watches.

• Amethyst
Amethyst is a variety of quartz which is purple in colour due to impurities including transition metals such as iron. Discussing the similarities in crystal shape may help to convince children that this is indeed the same mineral apart from these impurities.

• Tiger’s Eye
It is thought that Tiger’s Eye is a gemstone which used to be blue asbestos (also called crocidolite), a fibrous mineral. During metamorphism, the asbestos is dissolved, and quartz precipitates in its place. This replacement allows the quartz to maintain the fibrous nature of the asbestos, and some of the iron oxide in the asbestos is left behind, and becomes an impurity in the quartz, giving it its golden colour. This leads to Tiger’s Eye’s appearance of parallel layers with slightly different golden shades that reflect the light in different ways.

• Agate
Agate is yet another form of silica (since the crust is mostly made up of silica it shouldn’t be too surprising that there are so many forms of it). This most commonly forms in water-filled cavities, where the silica precipitates on the walls of the cavity as layers of tiny crystals of quartz and moganite (a polymorph of quartz, so also SiO2). The multi-coloured banding is due to the different impurities in each band.

• Crackle Quartz
The colours in this crackle quartz are man-made. They are added by heating up quartz in dye.

• Flint/Chert
Flint and chert are very similar rocks, and I’m not actually sure which this is, as the only difference is the type of carbonate rock they form in. Flint forms in chalk, whereas chert forms in other rocks such as limestone. They are made from microcrystalline silica, with impurities and occasional fossils. It is not yet well-understood why the silica in these sediments has localised in this way, but is probably to do with dissolution and reprecipitation of silica in the buried sediments before the water has been squeezed out by compaction. It is thought that the shape of flint/chert nodules may be related to burrows in the sediment, and the source of the silica may be the skeletons of zooplankton such as radiolaria and sponge spicules which are both made from silica.
Flint and chert are also very interesting from an archaeological perspective due to two important properties. The first is their ability to be hammered (or “knapped”) into hard sharp blades, which led to them being used as the main material for tools by Stone Age people. The second is that when iron (or a mineral containing iron such as pyrite) is struck against flint, it produces sparks which can be used to light a fire. In general flint was better for these purposes than chert as it tends to be harder and more pure.

• Red Jasper
Jasper is an impure form of silica (SiO2), quite similar to chert (see Flint/Chert). Its colour varies according to the impurities, and the red colour in this jasper is probably due to ferric iron.

• Mookaite
Mookaite is an impure form of silica, and in fact a kind of chert (see Flint/Chert) formed from sediments which have a very high proportion of microfossils from zooplankton called radiolaria. Radiolaria make their tiny skeletons out of the silica dissolved in water.

• Magnetite
This mineral began its life with CHaOS with the label “Hematite”. However, not only does the colour seem slightly wrong, but, more importantly, hematite cannot be made into as strong a permanent magnet as the pieces in the box. Therefore Dave worked out that this must be another iron oxide, Magnetite.
Magnetite is an early mineral to crystallise from most magmas, and is stable to high temperatures, so can be found in small amounts in a lot of different kinds of rocks. When found naturally, magnetite may be weakly magnetised, but not to the same degree as those in the box – these have been artificially magnetised. However, in rocks with a lot magnetite, such as the basic igneous rocks of Skye, even the natural weak magnetism can be enough to offset compass needles and confuse hikers! Magnetite crystals have been found in the brains of some animals (including pigeons and us), and are thought to be useful for navigation.

• Lepidolite
Lepidolite is a lithium-rich mica, a major source of rubidium (which was first discovered in this mineral) and caesium. It can be found in pegmatites (granites with crystals larger than an inch, which is thought to be due to the presence of water), as well as other granites and high-temperature quartz veins. Like all micas (see Mica), it is a sheet silicate with one well-developed cleavage plane, and contains OH, so can only form from magmas in which at least a small amount of water has dissolved.

• Moonstone
Moonstone is a gemstone formed by the intergrowth of two kinds of feldspar – albite and orthoclase. These are minerals which crystallise during the cooling of magma. The two minerals may grow together in such thin flat layers that they are close enough to the wavelength of optical light to scatter it, producing a milky glow in the presence of light, said to resemble moonlight. This is called adularescence.

• Peacock Ore
Peacock ore, also called Bornite, has the chemical formula Cu5FeS4. It can be found in igneous rocks, contact metamorphic rocks (those heated up by a nearby igneous intrusion such as a magma chamber) and shales. It is an important copper ore and is iridescent.

The Rocks Box:
You might want to talk about rocks in general, and define what they are. (Ask something like “Can anyone describe what a rock is like?”) Depending on the age of the kids, they might be able to name rocks such as limestone, chalk and marble.(“Does anyone know the names of any types of rock?”) You could ask where rocks are used (old buildings mostly). You could say that newer buildings aren’t made of rocks as man-made materials like brick and concrete are cheaper.

Warning to geologists: you may have to resist the urge to murder people who some of the specimens as “just a normal rock”. The box should contain a key to these rocks and rock-forming minerals, and I will use the same numbering system.

A selection of the most common minerals which make up the majority of rocks in the Earth’s crust.

1. Quartz
See minerals section.
The specimen in the minerals box has a well-formed (“euhedral”) crystal shape, whereas this one has not – perhaps it was rounded while being transported by a river or something similar?

2. Feldspar (Microcline)
Feldspars are the most common mineral in the Earth’s crust – almost two thirds may be made from feldspars. They most commonly grow from magmas during crystallisation, but can crystallise in veins (e.g. as part of impure quartz veins) and some metamorphic rocks. They are also found in some sedimentary rocks, but as they are much softer than quartz, are worn down far more quickly in high energy environments. There are two main groups of feldspars: alkali and plagioclase feldspars. Alkali feldspars, such as microcline, tend to be pink in hand specimen, and are the pink blocky minerals found in some granites (but not the one in this box).

3. Mica (Muscovite) and
4. Mica (Biotite)
Micas are a group of sheet silicates, which means that their molecules are arranged in flat layers. This is why they have such a perfect cleavage (flat shiny surface, yes I know the word is hilarious) and grow in sheets. In fact, you can take tiny individual flakes off these micas, though I wouldn’t recommend it if you want them to last! Micas all have OH in their chemical formulae, and thus are described as hydrous minerals – this means that they require the presence of water to grow. If the micas form from cooling magma, the magma must have some dissolved water. For example, granite (but not the one in this box) often has muscovite and/or biotite. If the micas grow as a result of metamorphism (putting rocks under heat and pressure), the OH will come from other hydrous minerals such as chlorite, or even from mud.
Muscovite is a white mica, and biotite is a dark brown mica. They form in similar circumstances.

5. Calcite
See minerals section
This crystal is probably opaque due to small amounts of impurities.

6. Hornblende
Hornblende is a type of mineral called an amphibole. These have two cleavages at 56¬o to each other, which you can see if you look at one shiny surface of a crystal, and then rotate it through 56o in the correct direction. Hornblende is found in many intrusive igneous rocks, and some metamorphic rocks such as amphibolite.

Rocks formed by the solidification of magma in a magma chamber (intrusive) or on the surface of the Earth (extrusive). Magma = underground, lava = above ground

7. Pumice
Pumice is solidified magmatic froth. Magma has dissolved volatiles such as water and CO2¬, and these are more soluble under high pressure than low pressure. For a volcano to erupt there must be a build-up of pressure which forces the magma up to the surface. When the volcano begins to erupt, this pressure is rapidly release, and so the volatiles are no longer as soluble in the magma. This means that bubbles of water and CO2 will form, and as they magma and bubble travel up to the surface from the magma chamber, the pressure drops even more, so that more volatiles exsolve. Because the gas is much more compressible than magma, the bubbles grow even more as the pressure decreases. This creates a froth of magma and gas analogous to opening a fizzy drinks bottle.
If the magma travels quickly to the surface so that pressure is quickly released, and there is a high volatile content, and the magma is sufficiently viscous (e.g. andesite), then there may be so much gas expanding so quickly that the magma fragments, creating an explosive eruption, as ash and pumice are thrown high into the air, creating an eruption column which may rise high up into the atmosphere or fall back to earth and form an ash flow (also called a pyroclastic flow). The pumice is solidified froth, which cools so quickly that it is technically a glass (it has no mineral structure, see Obsidian). Pumice often has so much gas inside it that it floats on water (this one does), an some people use it to rub the dead skin off their feet, as all the vesicles (bubbles) make its surface very rough.
Examples of explosive volcanoes which erupted pumice include Vesuvius, Mount St Helens and Krakatoa. They tend to be subduction zone volcanoes (formed when old ocean floor sinks underneath another plate) because these have water-rich silica-rich (and therefore viscous) magmas. The other extrusive (erupted) igneous rocks in this box are from non-explosive volcanoes.

8. Obsidian
(Most children will have heard of this from Minecraft. In the game you can make it from adding lava to water, which is close to the truth, but emphasise that the game isn't factually accurate.)
Obsidian is also known as volcanic glass. During crystallisation, it takes time for the molecules to arrange themselves into a given crystal structure. If a liquid is cooled quickly enough (such as when window glass is made it is cooled quickly in water), there will be no time for this to happen, and so the resulting solid, called a glass, will have the molecular structure of a liquid despite being solid. Obsidian is made when lava cools very quickly and becomes a glass. This is most likely to happen to thin rhyolitic (very silica-rich) lava flows, as other compositions of lava would have to be cooled more quickly than could naturally happen. Obsidian is metastable at the Earth’s surface, and thus none has been found older than the Cretaceous, as, particularly in the presence of water, it changes into another rock type, perlite.
Obsidian is archaeologically interesting, because it is hard, and can easily be made sharp (I think the hand specimen already has some fairly lethal edges), and so was used by Stone Age man to make knives and other tools, though not as frequently as flint/chert due to its comparative rarity. It could also be polished to create rudimentary mirrors.

9. Basalt
Basalt is an extrusive igneous rock. This means that it formed from the cooling of lava which flowed from a volcano. It has cooled quite quickly to allow only small crystals to grow (you can make out some shiny surfaces under the magnifying glass, although the bigger crystals may have started to grow in the magma chamber – most of the crystals will be too small to see). The main difference between basalt, andesite and rhyolite is composition. Basalt is more iron and magnesium-rich and less silica-rich than rhyolite, and andesite is intermediate between the two. When magma cools in a magma chamber, iron-rich and silica-poor minerals crystallise first and fall to the bottom of the magma chamber. This means that the remaining magma becomes more silica-rich, iron-poor, magnesium-poor, and therefore lighter. The system becomes more complicated if new (SiO2-rich Fe-poor) magma is injected into the magma chamber, or if crustal material from the edges of the magma chamber (SiO2-poor Fe-rich) is assimilated into the magma. Thus in general magma moves slowly from basaltic to andesitic to rhyolitic composition until it completely solidifies, is erupted, or is mixed with new material. Magma of basaltic, andesitic or rhyolitic composition may erupt as lava.

10. Andesite
See Basalt for how extrusive igneous rocks are formed. Andesitic lava will only flow in a non-explosive eruption if it does not have a high volatile content (see Pumice).

11. Rhyolite
See Basalt for how extrusive igneous rocks are formed. Rhyolitic lava will only flow in a non-explosive eruption if it does not have a high volatile content (see Pumice). It forms a glass if cooled quickly (see Obsidian) and so only thick rhyolitic lava flows would cool to make rhyolite like that in the box. The larger crystals in this rock would have formed in the magma chamber, and didn’t fall to the floor of the magma chamber due to the high viscosity of rhyolitic magma (and perhaps also because of a similarity in density between the crystals and the magma). The rest of the rock is composed of tiny crystals (called groundmass) which formed when the lava cooled subaerially.

12. Granite
This is an intrusive igneous rock – a rock formed when magma trapped underground in a magma chamber cooled and solidified. Other intrusive igneous rocks include gabbro, which has the same composition as basalt, and diorite, which has the same composition as andesite. Granite has the same composition as rhyolite. Its larger crystal size is due to its slow cooling rate. There are three types of crystals to see in this granite:
• Quartz – the shiny grey ones
• Plagioclase feldspar – the dull white ones
• Hornblende – the shiny black ones
Alkali feldspars (such as microcline) and micas can also form in granites, but not in this specimen. All the minerals mentioned are in this box. Granites can have much bigger crystal sizes than this, and those with crystals more than 2.5cm in size are called pegmatites. These are thought to have grown in the presence of water.

When rocks experience high temperature and/or pressure they change, becoming metamorphic rocks. Four of the metamorphic rocks (mica schist, slate, gneiss, garnet schist) could have been made from the same protolith (original rock) – a (see Shale)
Very high pressure is usually associated with orogenic (mountain building due to continental collision) belts, whereas high temperature may be due to depth of burial, or the presence of a nearby magma chamber.

13. Mica Schist
Shale is made up of clay minerals and silt-sized particles (which are finer than sand) of other minerals such as quartz. The clay minerals become unstable at a lower pressure than the quartz, and so if shale put under sufficient heat and pressure, they will start to change into other minerals – usually micas. Micas tend to be aligned so that their cleavage is perpendicular to the direction of maximum compaction. All of the shiny minerals you can see in this rock are these micas.

14. Slate
A slate can also be made from the compaction of shale. This is a lower metamorphic grade than schist, the difference being that a slate has not experienced new crystal growth. The silt and clay minerals have aligned themselves in response to the pressure they have experienced, creating this characteristic slatey cleavage. It is this cleavage (a foliation along which the rock tends to break) which allows slate to be broken into the big flat slabs used for roof tiles.

15. Quartzite
Quartzite is metamorphosed sandstone. Since sand is often largely made up of quartz, it is simply formed by the recrystallisation of this quartz under high temperature and pressure.

16. Gneiss
Gneiss has undergone a higher grade of metamorphism than a slate or schist, but also made from shale. The high pressure and temperature conditions allow the rock to develop compositional banding perpendicular to the direction of maximum compaction. For this to occur, there must be both diffusion and recrystallisation happening. This allows the rock to have bands of white felsic (SiO2-rich, Fe-poor) and dark mafic (SiO2-poor, Fe-rich) material.

17. Garnet Schist
This is rather like the mica schist – it is also a metamorphosed shale in which recrystallisation has occurred, producing crystals visible to the naked eye. However, the large crystals in this specimen are of a mineral called garnet. This is a very dense mineral, and consequently is most likely to form under a lot of pressure (decently higher pressure than would be required to form the mica schist). This means that this garnet schist probably formed deeper in the Earth’s crust than the mica schist, but otherwise is rather similar in its formation.

18. Marble
Marble is metamorphosed limestone. Since limestone is mostly made up of carbonate minerals (calcite, dolomite etc), so marble is predominantly composed of carbonates which have recrystallised under high temperature and pressure. Kitchen surfaces are often made of Marble, so you can tell them they're eating off dead sea creatures to add interest.

Bits of sand, mud, dead organisms (which may become fossils) and other matter fall to the bottom of lakes, seas and rivers. As more layers of this sediment accumulate, the buried sediment gets squashed together, a lot of the water is squeezed out, forcing the sediments together into a sedimentary rock. During this compaction (which at a much lower pressure than metamorphism), minerals such as quartz and calcite that may be dissolved in the water may recrystallise between the sediments to form a cement, holding them together more securely.
Not all sedimentary rocks are made beneath bodies of water – for example, some sandstones are formed in deserts. However, they must all be formed by the compaction of grains of sediment together during burial.
If you can see layers in any of these rocks, it is probably the bedding, which is formed by the deposition of each new layer of sediment.

19. Sandstone
Sandstone is a rock composed almost entirely of sand grains which have been compacted together. They can form in a range of environments, including deserts, rivers, deltas, lakes or seas. Due to the currents or waves required to transport sand, softer minerals are often broken down before deposition, leading to very quartz-rich sand in many cases, as quartz is a very hard mineral.

20. Shale
Shale is a rock composed of silt-sized grains and clay which have been compacted together. They are formed in low energy environments, as currents and waves would wash away such small grains of sediment, and carry in and deposit heavier grains such as sand. This includes very slow rivers and deep lakes or seas.

21. Arkose Sandstone
This is a rock formed by the burial and compaction of sand with the softer minerals still intact. By definition, there should be at least 25% feldspar, but other minerals such as micas and calcite may also be present. To prevent the breakdown of these minerals physically or chemically, the sand must be deposited rapidly (for example at the base of a mountain range where a river slows down and spreads out, called an alluvial fan), preferably in an arid environment. A likely source rock for the required feldspar-rich sediments is an igneous rock such as granite.

22. Conglomerate
This rock is made up of pebbles, so must have been deposited in a particularly high energy environment, such as a beach with strong waves or a fast-flowing river. The pebbles are from fragments of rock which have been eroded, and then bashed into a smooth shape by the river or the waves. There may also be finer material if a river has quickly changed from being fast-flowing to slow-flowing.

23. Breccia
Breccia is made up of angular fragments of rock which have been eroded and deposited by a landslide or a river, without enough time spent in the river to be smoothed into rounded pebbles.

24. Limestone
Limestone is a sedimentary rock made up mostly of carbonates. This may be organic – from the shells of animals and the skeletons of microfossils – or inorganic – from calcium carbonate which has precipitated from sea/lake water where the water is oversaturated in calcium carbonate (this happens because to solubility of calcium carbonate in water is dependent on a number of things including pH and temperature).

Plant fossils:
The explanation for this experiment is included in the sheets in the box, and as part of the plant experiment (biology).

References for Images:
• The Rock Cycle – By Kreislauf_der_gesteine.png:Chd at de.wikipedia derivative work: Awickert (Kreislauf_der_gesteine.png) [CC-BY-SA-3.0 (], from Wikimedia Commons
• Map Plate Tectonics
• Earth Structure – adapted from Earth-G-force.png: derivative work: KronicTOOL (Earth-G-force.png) [CC-BY-SA-2.5 (], via Wikimedia Commons
• Geologic Time Scale – adapted from United States Geological Survey [Public domain], via Wikimedia Commons
• Fossil map – By [Public domain], via Wikimedia Commons
• Volcano X-Section – adapted from MesserWoland (own work created in Inkscape) [GFDL (, CC-BY-SA-3.0 ( or CC-BY-SA-2.5-2.0-1.0 (], via Wikimedia Commons
• Mosasaur Skeleton – By Mike Beauregard from Nunavut, Canada (Prepare To Meet) [CC-BY-2.0 (], via Wikimedia Commons
• Sea Urchin (echinoid) – Copyright ©2003 Daniel P. B. Smith. Licensed under the terms of the Wikipedia copyright.
• Straight Nautiloid – By Nobu Tamura (Own work) [GFDL ( or CC-BY-3.0 (], via Wikimedia Commons
• Crinoid Anatomy – By William I. Ausich ( [CC-BY-3.0 (], via Wikimedia Commons
Up-to-date Information
This experiment can be demonstrated by either just taking the samples that you feel confident talking about, or by following a certain story or activity. Some suggested activities are outlined below and can be found on laminated sheets and at the bottom of this page.

Sheet 1: Igneous Rocks (Box 1)
This is an activity that explains how igneous rocks (formed from molten magma, which is called magma below ground and lava above ground) can be made of similar starting materials but form different rocks because of different cooling rates.
Obsidian (B2) cools very fast, often in water, forming a volcanic glass rather than any crystals, essentially a frozen liquid (may know from Minecraft or Game of Thrones...)
Pumice (A2) cools quite fast in air, fine crystals that can only just be seen floats on water because of all the trapped air bubbles
Granite (F2) cools slowly underground, has big crystals made out of Quartz (A1 – used in microchips), Feldspar (B1) and Biotite Mica (D1)

Sheet 2: Sedimentary Rocks (Box 1)
This activity aims to show how sedimentary rocks form and how they turn into metamorphic rocks (morph means change) under high temperatures and pressures.
Sandstone (A4) – Quartzite (C3)
Mudstone (B4) – Slate (B3) – Schist (A3), very high T and P, silly word..., contains muscovite mica
Limestone (F4), made of crushed up dead sea creature shells – Marble (F3), often used in kitchen surfaces, we eat off dead sea creatures!

Sheet 3: Interesting Points (Box 2)
This sheet just offers some interesting rocks and fossils to look at and describe
F5, F6 – Trilobite, ancient ancestor of woodlouse, extinct, hard eyes made out of calcite CaCO3 in Box 1 E1
B5 – Mosasaurus tooth, a Mosasaurus is huge, as big as a room, extinct
A1 – Pyrite, fools gold, thought it was gold but actually FeS, Iron and sulphur (stinky egg smell)
B1 – Magnetite, magnetic
D1 – Agate, crystallised out from pools of dissolved silica in lava
E1 – Crackle Quartz, same as box 1 A1 but impurities give colour
C1 – Tektite, meteorite hits ground and mixes with rock on ground and explodes out across the globe

Other possible activities
Another option is to sort the Box 1 specimens into Igneous, Sedimentary and Metamorphic rocks, as well as minerals. Or these specimens could be placed on a schematic of the rock cycle.

Box 1: Main Rocks and Minerals Collection
Row 1 - Minerals
A1 – Quartz
B1 – Feldspar (Microcline)
C1 – Mica (Muscovite)
D1 – Mica (Biotite)
E1 – Calcite
F1 – Hornblende
Row 2 – Igneous Rocks
A2 – Pumice
B2 – Obsidian
C2 – Basalt
D2 – Andesite
E2 – Rhyolite
F2 – Granite
Row 3 – Metamorphic Rocks
A3 – Mica Schist
B3 – Slate
C3 – Quartzite
D3 – Gneiss
E3 – Garnet Schist
F3 – Marble
Row 4 – Sedimentary Rocks
A4 – Sandstone
B4 – Shale
C4 – Arkose Sandstone
D4 – Conglomerate
E4 – Breccia
F4 – Limestone

Box 2: Rocks, minerals, gem stones and Fossils
A1 – Pyrite (Fool’s Gold)
B1 – Magnetite
C1 – Tektite and Flint
D1 – Agate
E1 – Crackle Quartz (and Mookaite?)
F1 – Quartz
A2 – Calcite
B2 – Aragonite
C2 – Marble
D2 – Tiger’s Eye, Jasper, Mookaite?
E2 – Peacock Ore
F2 – Amethyst?
A3 – Turtle Shell
B3 – Nautiloid (straight-shelled)
C3 – Gastropod
D3-4 – Unknown?
E3-4 – Amethyst
F3-5 – Assorted Gems
A4 – Shark Tooth
B4 – Shark Teeth
C4 – Echinoid
A5 – Crinoid stem
B5 – Mosasaurus Tooth
C5 – Coral
D5 – Bivalves
E5-6 – Woolly Mammoth Bone
F5-6 – Trilobite
A6 – Brachiopod
B6 – Dinosaur Bone
C6 – Ammonites
D6 – Ammonoids

Risk Assessment
Date risk assesment last checked: 
Tue, 19/12/2017
Risk assesment checked by: 
Date risk assesment double checked: 
Wed, 27/12/2017
Risk assesment double-checked by: 
Risk Assessment: 

Sets of small rock, mineral and fossil samples, and a magnifying viewer.

Possible choke hazard for small children with the smallest pieces
Dropping fossils could cause injury to feet.
Dropping fossils may cause them to shatter, producing shale dust
Fossils could be sharp and cause cut injury

Ensure that items are not in the reach of small children.
Hold fossils over a table or close to the floor (i.e. when sitting on the floor).
Keep fossils in clear plastic bags for protection and to prevent dust if breakage occurs.
Make sure fossils have no sharp edges.

Contact first aider if injury occurs.