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Lesson 11: Density
Lesson 12: Luster
Lesson 13: Fluorescence
Lesson 14: Magnetism
Lesson 15: Making Limestone
Lesson 16: Sandstone
Lesson 17: Popcorn Rocks
Lesson 18: Igneous Rocks
Lesson 19: Metamorphic Rocks

Quick Links:
Geology 1
Geology 3

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Lesson 11: Density

Density can be found by weighing an object and dividing by the volume of the object, and for geologists, is the same thing as specific gravity. Water has a density of 1, which means that 1 gram of water takes up 1 cubic centimeter of space. Specific gravity is a number you get when you divide the density of an object by the density of water, which happens to be 1 gram/cm3.

Materials

Measuring cup that has graduation marks for milliliters (mL)
Scale that measures in grams
Rock samples (in the video: quartz, meteorite, pumice)

Download worksheet and exercises

The specific gravity (also called the “s.g.” or “SG”) of a mineral or rock is how we compare the weight of the sample with the weight of an equal volume of water. Low specific gravity substances, like pumice (0.9), are not very dense. High specific gravity substances, like for gold (19.3), are very dense. If the specific gravity is less than 1, it will float on water.

Density is a way to measure two different minerals that might be exactly the same size, but their weights are different. Minerals with a metallic luster tend to be heavier. You’ll find variations for SG within the same minerals due to impurities of the mineral. Along those lines, this test can’t be done for material that is embedded within a rock, only for a single sample.

Here are a few examples for you to compare your samples with:

Amber 1.1
Quartz 1.5
Obsidian 2.5
Amethyst 2.6
Diamond 3.5
Hematite 5.05
Pyrite 5.1
Gold 19.3

Label and number each of your samples and record this on your data table.
Weigh each sample and record the information on your table.
Fill your cup with water and note the level.
Completely submerge your sample and read the new water height.
Subtract #4 from #3 answers to get the amount of water your sample displaces. Record this in your data table.
Find the volume of water displaced for every sample.
Divide the mass of the object by the volume to find the density: ρ = m / V with the units of grams / mL
Note: 1 mL = 1 cm³

Exercises

In your data table, which number was the same for every trial run?
What is the equation for finding density?
How did you find the volume of the rock?

Lesson 12: Luster

Luster is the way a mineral reflects light, and it depends on the surface reflectivity.

Materials

Sunlight
Rock samples (in the video: pyrite, fluorite, and serpentine)

Download worksheet and exercises

Every mineral has a particular luster, but some have different luster on different samples. Since it’s gauged by eye and not a scientific instrument, there’s quite a lot to be left to the observer when describing it. Luster is not usually used to identify minerals, since it’s so subjective.

That said, it is useful when describing a sample’s surface, so hold up yours to the light and use the descriptions below to find the one that best describes what you see.

Metallic or splendent luster are found in highly reflective minerals, like gold.
Submetallic luster is found in minerals that have a similar luster to metal, but it’s a bit duller and less reflective. These minerals are opaque and reflect light well. You’ll find submetallic luster in the thin splinter sections of minerals, such as sphalerite, cinnabar, and cuprite.
Vitreous or glassy luster describes 70% of all minerals, and they have the luster of glass. Quartz, calcite, topaz, beryl, tourmaline, and fluorite are examples of glassy luster.
Adamantine lusters (brilliant, like a cut diamond) are for transparent materials that show a very bright shine because they have a high refractive index.
Resinous lusters are usually yellow, orange, or brown minerals that have high refractive indices (like the way sunlight goes through honey).
Silky lusters have very fine fibers aligned in parallel, so it looks like a cloth of silk. Minerals like asbestos, ulexite, and a variety of gypsum called satin spar all have silky luster. If a sample has fibrous luster, it is coarser than a silky luster.
Pearly luster minerals look like the way light reflects off pearls, like the inside an oyster shell. These types of minerals have perfect cleavage, like muscovite and stilbite. Mica also has a pearly luster. Some pearly luster minerals also have an iridescent hue.
Greasy or oily luster looks like fat, and is found in minerals that have a lot of microscopic inclusions, like opal and cordierite. Most greasy luster minerals also feel oily.
Pitchy luster looks a lot like tar, and is found in radioactive minerals.
Waxy luster resembles wax, the way jade and chalcedony look on their surface.
Dull or earthy luster minerals have very little or no luster at all, because they have a surface that scatters the light in all directions, like with Kaolinite. Some geologists say that earthy luster means less luster than dull, but it’s really a close call between the two.

When light strikes a surface, it can be reflected off the surface, like a mirror, or it can pass through, like a window, or both. Metallic luster has most of the light bouncing off the surface, whereas calcite has most passing through the mineral. When light travels through a mineral, it refracts, or changes speed, as it crosses the new material boundary. This is what makes the luster appear different for different materials.

Refraction is how light bends when it travels from one substance to another. When light moves through a prism, it bends, and the amount that it bends is seen as color that comes out the other side. Each color represents a different amount of bending that it went through as it traveled through the prism.

Label and number each of your samples and record this on your data table.
Hold your mineral in the sunlight.
Use the list to find the word that best describes what you see. Look particularly on your sample for a surface that is clean and not tarnished, discolored, or coated. Look at cleaved surfaces and on uneven parts.

Metallic
Submetallic (duller than metallic)
Vitreous or glassy
Adamantine (like a cut diamond)
Resinous (like honey)
Silky (like a silk cloth)

Pearly
Greasy or oily
Pitchy (like tar)
Waxy (like a candle)
Dull or earthy

Record your observations in the data table.

Exercises

What is refraction?
Feldspar has perfect cleavage on two surfaces but fractured on a third. What kind of luster would you say it has?
What type of luster is found on mica?

Lesson 13: Fluorescence

Fluorescent minerals emit light when exposed to ultraviolet (UV) light, usually in a completely different color than when exposed to white light. UV is invisible to the human eye, and is the wavelength of light that is responsible for sunburns.

Materials:

Longwave UV light
Sunlight
Rock samples (The four samples at the end of the video are: top left is opalite, top right is calcite, bottom left is norbergite, bottom right is calcite & willemite.)

Download worksheet and exercises

Stars, including our sun, produce all kinds of wavelengths of light, even UV. The UV minerals in this lab contain a substance that reacts with light. It takes the UV light from the sun and then re-emits it in a different wavelength that’s visible to us.

When a particle of UV light hits an atom in the mineral, it collides with an electron which makes the electron jump to a higher, more energetic state that is a bit further from the center of the atom than the electron is used to. That’s how energy gets absorbed by an atom. The amount of energy an electron has determines how far from the atom it has to be.

The electron prefers being in its lower state, so it relaxes and jumps back down, and when it does, it transfers a blip of energy away. This blip of energy is the light we see emitted from the UV mineral. This process continues as long as we see a color coming from the mineral under the UV light.

There are two different types of UV wavelengths: longwave and shortwave. Some minerals fluoresce the same color when exposed to both wavelengths, while others only fluoresce with one type, and still others fluoresce a different color depending on which it’s exposed to. Minerals fluoresce more notably with shortwave UV lamps, but these are more dangerous than longwave since they operate at a wavelength that also kills living tissue.

Shortwave UV lamps and lights should only be operated by an experienced adult. Never use a shortwave light when children are around.

Most minerals do not fluoresce, but in the ones that do, there are either small impurities that fluoresce (called “activators”) or the pure substance itself fluoresces (although this is rare). For a mineral to fluoresce, the impurities present must be in just the right amount. For example, red fluorescent calcite from Franklin, NJ, USA is activated by manganese that’s present, but only if there’s about 3% of it in the mineral. If there’s more than 5% or less than 1% manganese, the sample won’t fluoresce at all. It’s the amount and type of the impurities that determines the color and intensity of the fluorescence.

Fluorescence is not a reliable way to identify a mineral, since some samples will fluoresce with different colors even though they are all the same mineral. Fluorescence is used to determine where the mineral came from, since the colors that the minerals fluoresce usually match the original location of the mineral.

Phosphorescence is when a sample glows even after you turn off the UV light source. This is the type of glow you’ll find in “glow in the dark” toys, where the light slowly fades after you turn off the light. Atoms continue to emit light even after the electrons return to their normal energy states. While it looks like seconds to minutes that the glow lasts, some samples have been found to phosphoresce for years using highly sensitive photographic methods. Only a few minerals phosphoresce, such as calcite from Terlingua, Texas.

Label and number each of your samples and record this on your data table.
Hold your mineral in the sunlight and record the color in the data table.
Go inside and turn off the lights. Hold your sample under a longwave UV light and record the colors that you see.
Complete the data table.

Aragonite
Hackmanite
Calcite
Fluorite
Opalite
Calcite & willemite
Tremolite
Resinous coal
Wernerite

Aragonite
Termolite
Wiollemite
Opalite
Chalcedony
Calcite & willemite
Talc
Resinous coal
Norbergite
Calcite

Exercises

What wavelength is shortwave UV? Longwave UV?
How is fluorescence different from phosphorescence?
Name two minerals that fluoresce in both shortwave and longwave UV light.

Lesson 14: Magnetism

A magnetic field is the area around a magnet or an electrical current that attracts or repels objects that are placed in the field. The closer the object is to the magnet, the more powerfully it’s going to experience the magnetic effect. Nearly all minerals that are magnetic have iron as a component.

Materials:

Magnet
Rock samples (samples in the video that stuck to the magnet are lodestone [which is the magnetic form of magnetite] and meteorites)

Download worksheet and exercises

Minerals can become attracted to a magnetic field if they are heated to a certain temperature. These minerals become ferromagnetic after heating them up. Some minerals also act as magnets when they are heated, but this effect is only temporary for as long as the mineral stays at that temperature.

Magnetism is a very useful way of identifying a mineral, because it’s so precise. When testing for magnetism, you’ll get better results if you use the strongest magnet you can find. You’ll find minerals that respond to magnets (without heating them up first) are metallic-looking samples.

Most student-grade geology books refer to minerals that are attracted to magnetic fields as “magnetic,” which leads to confusion because there’s a difference between being “magnetic” (acting as a magnetic field) and being “attracted to magnetic fields.” When you fill out your observations in the data table, keep this in mind when you write down what you see by using the words “magnetic” or “attracted to a magnetic field.”

Label and number each of your samples and record this on your data table.
Hold your mineral close to the magnet and observe how strongly it is attracted to the magnet. How far away do you have to be to start influencing the sample?
Complete the data table.
There are several magnetic properties that geologists use to specify the type of magnetism within a mineral:
- Ferromagnetism is the kind of magnetism you’ll see in magnetite and pyrrhotite, as these have strong attraction to magnetic fields.
- Paramagnetism is a weak attraction to magnetic fields, such as with the minerals hematite and franklinite.
- Diamagnetism occurs in only one mineral, bismuth, which means it’s repelled from magnetic fields.
- Magnetism is found in only one mineral called lodestone, which is the magnetic version of magnetite. It’s really rare, since it’s only found in a couple locations in the entire world. Lodestone is weakly magnetic, but if you drop small paperclips, staples, and iron filings onto a piece, they’ll stick.

Exercises

Is lodestone the same as magnetite?
Which mineral is repelled from any magnetic field?
Which element is usually present in minerals that have magnetic properties?

Lesson 15: Making Limestone

Out of all the kinds of sedimentary rocks, limestone makes up 10% by volume. People have used limestone in architecture like the Great Pyramids, castles in Europe, and in early 20th century buildings like banks and train stations. Today we use it as white filler in toothpaste, to build roads, make tiles, in cosmetics, and added to breads and cereal as a cheap source of calcium.

Materials:

Goggles
Distilled white vinegar (you only need a drop, so use a medicine dropper)
Funnel
Straw
2 water bottles
2 paper napkins
Calcium hydroxide (also known as “lime”) This chemical is irritating to skin and eyes, so use your goggles and gloves when handling since it’s a dust. This chemical is toxic and should only be handled by an adult. Find safety information under MSDS Calcium Hydroxide

DO NOT ALLOW CHILDREN TO DO THIS EXPERIMENT. Limewater is TOXIC. This experiment is for demonstration purposes only by an adult.
STUDENTS: You can watch the video and complete the data table and exercises if you’re not able to have an adult do this for you

Download worksheet and exercises

Limestone is a sedimentary rock that is mostly calcium carbonate, and some amazing fossils have been found in limestone. In our experiment today, we are doing a simple chemistry experiment that produces calcium carbonate as the product. The calcium carbonate is created from a chemical reaction of the carbon dioxide from your breath mixed with calcium hydroxide. Only 4-5% of your breath is converted into carbon dioxide, so it takes awhile to get enough carbon dioxide through the solution to form the calcite crystals and see the color change happen.

Put on your goggles and gloves.
Fill one of your water bottles partway with water.
Add a spoonful of calcium hydroxide.
Cap the calcium hydroxide and store safely away.
Place the cap on the water bottle and shake up the solution. Set aside and do not disturb for several minutes.
Fold your napkin into a shape that will fit into your funnel. This is a liner for your funnel that will catch the solids as they are poured into the funnel.
Put a little water into your funnel to dampen the paper napkin liner.
Place the second (empty) water bottle under the funnel.
Pour the limewater solution through the funnel. Don’t pour the sludge at the bottom into the funnel.
Insert a straw into the water bottle with the strained limewater.
Write down the color of the solution. Is it cloudy? Clear?
Blow gently into the straw for several minutes until you see a color change. DO NOT INHALE. Limewater is very toxic!
What color did the color change to? Record your observations in the data table.
Test the calcite by pouring the solution through a new paper funnel.
Place a drop of acetic acid (distilled white vinegar) on the calcite crystals and watch for a slight reaction.

Exercises

What element is present in both calcium carbonate and your breath when you exhale?
Why aren’t kids allowed to do this experiment? What’s the danger?
Where can you find safety information for chemicals?

Lesson 16: Sandstone

Sandstone is a common sedimentary rock that’s composed of quartz crystals cemented together by silica, calcium carbonate, clay or iron oxide. Fossils are often found in sandstone.

Materials

2 paper cups
Water
Popsicle stick
Sand
Plaster of Paris
Shell (something to make a fossil impression of)
Scissors

Download worksheet and exercises

One way geologists classify sandstone is by the amount of quartz, feldspar, and lithic grains it contains. Quartz sandstone is composed of more than 90% quartz grains, while feldspathic sandstones has less than 90% quartz, but more feldspar than lithic grains. Lithic sandstones have both less than 90% quartz and more lithic grains. In addition, if a geologist calls a sample “clean sandstone,” then it means that there are tiny holes in the sample, like pores. They’ll add the word “arenite” to the name, so you might hear “quartz arenite” which means a sandstone that has more than 90% of its grains as quartz and is also porous.

Pour enough sand to cover the bottom of one of the cups.
In the second cup, make a 1:1 mixture of Plaster of Paris and water. (You can add food dye to make the plaster more visible when layered, but this is optional.)
Stir to combine with the popsicle stick.
Pour a layer right on top of the sand.
Add more sand to the first cup.
Now add more plaster.
Continue adding in layers until you have at least six layers (three of each), but you can do more if you have enough room and materials.
Do not mix the layers.
Cover the last layer with sand.
If you’re making a fossil impression, first rub vegetable oil over it (so the sand doesn’t stick) and press firmly into place without twisting or pushing too hard. Allow it to dry for 24 hours.
When it’s dry, carefully remove the fossil on top and see the impression you’ve made!
Tear away the cup to see the different layers of your homemade sandstone.

Exercises

What elements is calcium carbonate made out of? (Carbon and oxygen.)
How does this experiment look like sandstone? (The tiny grains of sand are glued together by the Plaster of Paris.)
What do you know about a feldspathic arenite sample? (The sample has less than 90% quartz, but more feldspar than lithic grains, and it’s porous.)

Lesson 17: Popcorn Rocks

Popcorn rocks are different than regular dolomite samples because they have a lot more magnesium inside. This was first discovered by a geology professor in the 1980s who was dissolving the limestone around fossils he was studying in his rock samples. When he placed samples of this type in the acid to dissolve, it didn’t dissolve but instead grew new crystals!

Materials:

“Flowering Rock” dolomite samples
Distilled white vinegar (acetic acid)
Disposable cup or glass jar
Penny
Nail
Streak plate
Water in a graduated container
Scale that measures in grams
Longwave UV light source
Sunlight

Download worksheet and exercises

Dolomite is made of calcium magnesium carbonate (CaMg(CO₃)₂ and is both a mineral and a rock. Dolomite comes in all kinds of colors, including white, gray, pink, peach, yellow and orange … even colorless. Dolomite gives a white streak, which is hard to see on a white streak plate, and the hardness ranges from 3.4 to 4 on the Moh’s hardness scale. Specific gravity for dolomite is 2.8 to 3, with a vitreous (glassy), pearly luster and rhombohedra cleavage on two planes and conchoidal fracture on the third. It’s brittle (think tenacity), and is usually found around limestone. Dolomite is a chemical rock, since it reacts to acid. Dolomite fluoresces bluish-white when placed under a longwave UV light, and pink when exposed to a shortwave UV light.

You’re first going to classify dolomite and test it for certain properties, and then you’ll grow crystals all over it. If you don’t have a UV light, skip it and perform the rest of the tests.
Complete the first data table for the sample before following the instructions on the video. You are looking for the color, streak, hardness, density, luster, cleavage, fracture, tenacity, acid reaction, and fluorescence.
Don’t wash your dolomite sample. You want the dust layer on top so the crystals start growing more quickly.
Place the sample in your glass jar.
Pour the vinegar into the cup (not directly on your sample) until it’s nearly submerged.
Move your experiment to a warm location.
Observe your rock formation over the next week and record your observations in the second data table. You can opt to take pictures and paste them into the data table.
When all the vinegar has evaporated, remove the sample and put on display (after recording your last observation).

Exercises

What would happen if you warmed the vinegar first, and placed it on a heating pad during your experiment?
What is it in the dolomite samples that make the aragonite crystals grow?
What else can you try instead of vinegar?

Lesson 18: Igneous Rocks

Igneous rocks are classified as being extrusive or intrusive. An intrusive rock has a courser grain texture without a magnifier. Extrusive rocks need a magnifier to see the finer grains that make up the rock. Some extrusive rocks, like obsidian, need a microscope to see the fine grains.

Download worksheet and exercises

Clastic sedimentary rocks are fragments of other rocks. Geologists look at the tiny particle grains that make up the rock when they name the rock. For example, mudstone is named for its tiny particles of mud and clay, and sandstone is made up of larger grains of sand. The conglomerate rocks look like they are made up of pebbles. Siltstone under a strong magnifier show microscopic grains.

Number and label your samples with your data table.
Take your hand magnifier and look closely at each sample and record the color information on the data table.
Use a dropper to take vinegar out of its bottle.
Drop a few drops onto your sample and watch for a reaction. If you see a reaction, note this in the data table and classify the rock as a chemical rock, not a clastic rock.
Wipe your samples dry with a clean, damp cloth.
Test the hardness of your sample with the nail and record it in your data table using Mohs’ Hardness Scale.

Exercises

Give three types of clastic sedimentary rocks.
How can you tell a clastic from a non-clastic rock?
Does hardness determine a clastic rock? If so, what hardness do you expect a clastic rock to have?

Lesson 19: Metamorphic Rocks

Metamorphic rocks are classified by as being foliated or non-foliated. Foliated rocks have layers, like bands around the rock. Non-foliated rocks dont have any layers are are solid-looking throughout, although they might have crystals here and there. If the crystals are aligned to form a layer, then its a foliated rock.

Download worksheet and exercises

Number and label your samples with your data table.
Take your hand magnifier and look closely at each sample and record the color information on the data table.
Use a dropper to take vinegar out of its bottle.
Drop a few drops onto your sample and watch for a reaction. If you see a reaction, note this in the data table and classify the rock as a chemical rock, not a clastic rock.
Wipe your samples dry with a clean, damp cloth.
Test the hardness of your sample with the nail and record it in your data table using Mohs’ Hardness Scale.

Exercises

Give three types of clastic sedimentary rocks.
How can you tell a clastic from a non-clastic rock?
Does hardness determine a clastic rock? If so, what hardness do you expect a clastic rock to have?

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