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geology1You are about to become a real geologist as you explore our dynamic planet. Youll learn about the world of rocks, crystals, gems, fossils, and minerals by moving beyond just looking at pretty stones and really being able to identify, test, and classify samples and specimens you come across using techniques that real field experts use. While most people might think of a rock as being fun to climb or toss into a pond, you will now be able to see the special meaning behind the naturally occurring material that is made out of minerals by understanding how the minerals are joined together, what their crystalline structure is like, and much more.

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We’re going to cover the following scientific concepts:

  • Rocks
  • Fluorescence
  • Minerals
  • Chemistry & Composition
  • Gems
  • Geology Field Trips
  • Crystals
  • Building Materials
  • Identification techniques
  • Real Geology Projects
  • Earthquakes

Step 1:

We’re about to dive into a comprehensive course that teaches the big ideas behind rocks, minerals, and the science of geology. Soon you’ll learn how to burn coal, fluoresce minerals, chemically react rocks, streak powders, scratch glass, and play with atomic bonds as they learn how to be a real field geologist. Throughout this course, we’re going to be talking about the chemical composition (what elements rocks are made of), so you’ll really understand chemistry and geology both!

To get started learning, print out this workbook, which includes a complete shopping list inside. Youll be filling out this workbook out as you work through the course. The material list inside the worksbook is materials just for the experiments covered in the introductory video. For materials for the entire curriculum, click the link below.

Click here for the shopping list for this course.

Step 1a (Optional): Teleclass Replay plus Bonus Content

Heres a replay of the original teleclass we did in geology together, plus additional bonus content we didnt get to during our class time:

Step 2:

Download the curriculum guidebook for the set of videos below. You can watch the videos below in order. If you have the materials to do the experiments, feel free to do the experiments along with me. If not, just watch the videos so you still get the experience of what the experiment is all about. Some of the experiments have additional worksheets you can print out and fill in as you work through the experiment. At the end of the course, you can print out this assessment packet to use to see how much your child has picked up in the course!

Lesson 1: Introduction
Lesson 2: Minerals
Lesson 3: Storing
Lesson 4: Color Streak
Lesson 5: Mohss Hardness Test
Lesson 6: Cleavage and Fracture
Lesson 7: Acid Test
Lesson 8: Sedimentary Rocks
Lesson 9: Burning Coal
Lesson 10: Tenacity

Quick Links:
Geology 2
Geology 3

Lesson 1: Introduction

Were about to dive into a comprehensive course that teaches the big ideas behind rocks, minerals, and the science of geology. Soon youll learn how to burn coal, fluoresce minerals, chemically react rocks, streak powders, scratch glass, and play with atomic bonds as they learn how to be a real field geologist.

Everything is matter. Well, except for energy, but that’s everything else. Everything you can touch and feel is matter. It is made up of solid (kind of) atoms that combine and form in different ways to create light poles, swimming pools, poodles, Jell-O and even the smell coming from your pizza.

All matter is made of atoms. Shoes, air, watermelons, milk, wombats, you, everything is made of atoms. Hundreds and billions and zillions of atoms make up everything. When you fly your kite, it’s atoms moving against the kite that keep it in the air. When you float in a boat, it’s atoms under your boat holding it up.

My definition of an atom is: the smallest part of stable matter. There are things smaller than an atom, but they are unstable and can’t be around for long on their own. Atoms are very stable and can be around for long periods of time. Atoms rarely hang out on their own, though. They are outgoing and usually love to get together in groups. These groups of atoms are called molecules. A molecule can be made of anywhere from two atoms to millions of atoms. Together these atoms make absolutely everything, including the minerals, crystals, and rocks we’re about to study.

Lesson 2: Minerals

A periodic chart has a bunch of boxes. Each box represents one element. In each box is a ton of information about each element. All atoms are made from the same stuff; it’s just the amount of stuff that makes the atoms behave the way they do.

If you look at a periodic table you will notice that there will be about 112 to 118 different elements (this will vary depending on how recently the table was created). About 90 of those occur naturally in the universe. The other ones have been man-made and are very unstable. So imagine: Everything in existence, in the entire universe, is made of one or several of only about 90 different types of atoms. Everything, from pianos to pistachios are made from the same set of 90 different Legos!

Now, if you find that amazing, listen to this: Almost everything in the universe is mostly made of only twelve different kinds of atoms! But wait, there’s more.

All living things are mostly made of only five different kinds of atoms! Five! You and a hamster are made of the same stuff! All living and once-living things are made mostly of carbon, hydrogen, oxygen, nitrogen, and calcium. Ta daa! Those are the ingredients for life. Put ‘em in a bowl, stir and voila, you can make your own penguin.

Okay, obviously it’s not that easy. It takes a lot more than that to make life, but at least now you know the ingredients. An easy way to remember the main ingredients for living things is to remember the word CHONC. Each letter in CHONC is the first letter in the 5 elements carbon, hydrogen, oxygen, nitrogen and calcium.

One last interesting thing to think about here: Of all the atoms in the entire universe, 90% of them are hydrogen. Only 10% of the entire universe is made up of anything other than hydrogen.

Throughout this course, were going to be talking about the chemical composition (what elements rocks are made of), so youll really understand chemistry and geology both!

Lesson 3: Storing

Minerals are pure chemical substances, made up entirely of one molecule through and through. Examples of minerals are everywhere. Rock salt is a mineral called halite. Fool’s gold is a mineral called pyrite. They are made of a single substance and nothing else. Rocks are composed of two or more minerals. We’re going to study rocks, minerals, crystals, and more in our unit on geology!

Lesson 4: Color Streak

You will be able to identify minerals by their colors and streaks, and be able to tell a sample of real gold from the fake look-alike called pyrite.

Materials

  • 1 handheld magnifying lens
  • Unglazed porcelain tile
  • Rock samples (the ones in the video are: graphite, pyrite, talc, iron, and jasper)

Download worksheet and exercises

Every mineral has a set of unique characteristics that geologists use to test and identify them. Some of those tests include looking at the color of the surface, seeing if the mineral is attracted to a magnet, dripping weak acids on the rock to see if they chemically react, exposing them to different wavelengths of light to see how they respond, scratching the rocks with different kinds of materials to see which is harder, and many more. There are more than 2,000 different types of minerals and each is unique. Some are very hard like diamonds, others come in every color of the rainbow, like quartz and calcite, and others are very brittle like sulfur.

The color test is as simple as it sounds: Geologists look at the color and record it along with the identification number they’ve assigned to their mineral or rock. They also note if the color comes off in their hands (like hematite). This works well for minerals that are all one color, but it’s tricky for multi-colored minerals. For example, azurite is always blue no matter where you look. But quartz can be colorless, purple, rose, smoky, milky, and citrine (yellow).

Also, some minerals look different on the surface, but are really the same chemical composition. For example, calcite comes in many different colors, so surface color isn’t always the best way to tell which mineral is which. So geologists also use a “streak test”.

For a streak test, a mineral is used like a pencil and scratched across the surface of a ceramic tile (called a streak plate). The mineral makes a color that is unique for that mineral. For example, pink calcite and white calcite both leave the same color streak, as does hematite that comes in metallic silvery gray color and also deep red. This works because when the mineral, when scratched, is ground into a powder. All varieties of a given mineral have the same color streak, even if their surface colors vary. For example, hematite exists in two very different colors when dug up, but both varieties will leave a red streak. Pyrite, which looks a lot like real gold, leaves a black streak, while gold will leave a golden streak.

The tile is rough, hard, and white so it shows colors well. However, some minerals are harder than the mineral plate, like quartz and topaz, and you’ll just get a scratch on the plate, not a streak.

  1. Number your rock samples by placing them on your data table.
  2. Using your data table, record the color of each sample.
  3. Now use your streak plate. Take a rock and draw a short line across your streak plate (unglazed porcelain tile).
  4. Record the color of the streak in your data table. Are there any surprises?

Exercises

  1. What does it mean if there’s no streak left?
  2. Give an example of a kind of rock that leaves a streak a different color than its surface color.
  3. What is a mineral that appears in two different colors, yet leaves the same color streak?

Lesson 5: Mohss Hardness Test

By the end of this lab, you will be able to line up rocks according to how hard they are by using a specific scale. The scale goes from 1 to 10, with 10 being the hardest minerals.
Materials

  • Steel nail
  • Penny
  • Small plate of glass (optional)
  • Rock samples (minerals in the video: talc, selenite, calcite, fluorite, apatite, feldspar, quartz)

Download worksheet and exercises

The sample’s hardness is determined by trying to scratch and be scratched by known materials, like pennies, steel, glass, and so forth. If the material leaves a mark on the mineral, then we know that the material is harder than the mineral is. We first start with a fingernail since it’s easy to use and very accessible. If it leaves a mark, that means that your fingernail is harder than the mineral and you know it’s pretty soft. Talc is one of the softest minerals, making it easy to scratch with your fingernail.

However, most minerals can’t be scratched with a fingernail, so we can try other objects, like copper pennies (which have a hardness of 2.5-3.5), steel nail (3.5-5.5), steel knife (5.5), and even quartz (7). The most difficult part of this experiment is keeping track of everything, so it’s a great opportunity to practice going slowly and recording your observations for each sample as you go along.

  1. Number your samples on the data table and place each rock on the table. If you have the same samples listed above, you can scratch each rock with every other rock to find where they are on the Mohs’ Hardness Scale, where 1 is the softest and 10 is the hardest:
    Mohs’ Scale of Hardness Talc
  1. Selenite
  2. Calcite
  3. Fluorite
  4. Apatite
  5. Feldspar
  6. Quartz
  7. Topaz
  8. Corundum
  9. Diamond
  • If you don’t have one of each from the following scale (at least up to quartz), then you’ll need to do this experiment a different way – the way most geologists do it in the field. Here’s how:
  • Scratch one of the rocks with your fingernail. If you can leave a mark, then write “Y” in the second column of the data table. Now skip over to the last column and estimate the hardness to be less than 2.5.
  • If you can’t scratch it with your fingernail, try using the mineral to scratch a copper penny. If it doesn’t leave a mark on the penny, skip over to the last column and estimate the hardness to be between 2.5-3.5.
  • If it does leave a scratch on the penny, then try scratching the mineral with a steel nail. If the nail leaves a scratch, skip over to the last column and estimate the hardness between 3.5-5.5.
  • If you can’t scratch the sample with the nail, see if the mineral can make a scratch on the plate glass. Glass has a hardness of 6-7. If it doesn’t make a scratch on the glass, then it’s between 5.5-6.5. If it does, it’s higher than 6.5. For example quartz will make a scratch on the plate, and its hardness has been recorded at 7.

Exercises

  1. If a mineral scratches a penny but doesn’t get scratched by a nail, can you approximate its hardness?
  2. Give examples of the hardest and softest minerals on the Mohs’ Scale.
  3. Is feldspar harder or softer than quartz?

Lesson 6: Cleavage and Fracture

Today, you’ll learn what to look for in a broken mineral. There are different names for the types of breaks that a mineral can experience. You’ll need to ask a few important questions during your investigation, like, “What is the difference between mineral cleavage and fracture?”

Materials

  • Mineral samples
  • Hand lens
  • Good lighting

Download worksheet and exercises

Cleavage and fractures are two properties that geologists test at the same time, both by observations. Using a hammer, geologists will break a mineral by studying how the mineral broke. They describe the way the surfaces look. Sometimes minerals break apart like they were stacked together in thin sheets. Other times they break off in large chunks, and the sides of each chunk are always at right angles. The way that they break into planes is called “cleavage.” Minerals can have cleavage in one direction, like mica, or two or three directions (like halite). The type of cleavage is also described using geometric terms. Halite has cubic cleavage because when it breaks, it looks like it’s made up of tiny cubes, while calcite has rhombic cleavage because it never breaks into right angles, but always in a rhombus, or diamond shape.

Fracture describes the surfaces that are broken but don’t break along plane lines. A mineral can have both cleavage and fracture, and some have either one or the other. Quartz has no cleavage, only fracture. Calcite has no fracture, only cleavage. Feldspar has both.

Geologist look for smooth surfaces, which can be (when viewed up close) cubes, triangles, or simple, flat plane surfaces. Always look for cleavage first, then fracture when making your data observations.

An easy way to look for cleavage is to hold the sample in sunlight and look for surfaces that reflect light and describe the surface in one of three ways for cleavage:

  • Perfect – the mineral breaks to reflect a clear, glass, or mirror-smooth surface.
  • Good – the mineral breaks to reveal a surface that reflects light, but may be dull in places.
  • Poor – the mineral breaks along clear planes and flat spaces are visible, but these are dull and could be ragged, and not very reflective.

Remember, a mineral can have more than one cleavage plane. For example, feldspar has two cleavages, one which is perfect and one which ranges from poor to good, depending on the sample. At first glance, you might not be able to tell feldspar from quartz, but if you look for cleavage, you’ll find feldspar has two planes of cleavage whereas quartz has none. Quartz will look like lots of broken surfaces that are not flat planes.

The way a mineral breaks depends on what the crystalline structure looks like. Here are some forms of cleavage:

  • Basal cleavage is cleavage on the horizontal plane, like mica. Basal cleavage samples can sometimes have their layers peeled away.
  • Cubic cleavage is found in mineral that have crystals that look like cubes., like with galena or halite.
  • Octahedral cleavage is found on crystals that have eight-sided crystals, like two pyramids with their bases stuck together. Look for flat, triangular wedges that peel off an octahedron, like in the mineral fluorite.
  • Prismatic cleavage is found in minerals that have four or more sides and are long in one direction, like aegirine, where the crystal cleaves on the vertical plane.
  • Rhombohedral cleavage is really my favorite, because it shows up in calcite so well due to its internal crystal structure, which is made up of hexagonal crystals. No matter where you look, there are no right angles to this cleavage – everything is at an angle.

Fracture can be described like this:

  • Conchoidal (like a shell, for example: obsidian)
  • Earthy (looks like freshly broken soil, like limonite)
  • Hackly or jagged (when a mineral is torn, like with naturally occurring silver or copper)
  • Splintery (looks like sharp, long fibrous points, like chrysolite)
  • Uneven (rough surface with random irregularities, like pyrite and magnetite)
  • Even or smooth (the fracture forms a smooth surface)
  1. You will begin by labeling each of the mineral samples, starting with 1. Make sure to keep track of these samples throughout the entire lab.
  2. Take the mineral samples and note which number it is on your observation data sheet.
  3. Using your hand lens, look carefully for little sparkles of surfaces that reflect light. These are the cleavage surfaces.
  4. In the space marked cleavage on your worksheet, label the cleavage as perfect, good, or poor. If there are no flat surfaces that are broken, write “none.” Some of your samples may have more than one cleavage. Make a note if this is the case.
  5. Now look for broken surfaces that are not flat. Place a check below the best category of fracture that the mineral shows. If there are no surfaces like this, mark “none.” If you are uncertain about either category, leave the section blank. It is better to record no information than to mark something that can mess up your data.

Exercises

  1. Which properties do geologists look for when they try to categorize a mineral? Circle all that apply.
    1. Color
    2. Shine
    3. Smell
    4. How it breaks
  2. If you break a sample of quartz and find that it has no clean surfaces of separation, what kind of cleavage does it show?
  3. True or false: A mineral can show more than one type of cleavage or fracture.
  4. What is a fracture called that is similar to glass?

Lesson 7: Acid Test

Your goal is to identify samples according to their reactivity with acid. Minerals that react are called chemical rocks, and minerals that don’t are called clastic rocks. Some chemical rocks contain carbonate minerals, like limestone, dolomite, and marble which react with the acid.
Materials

  • Acetic acid (plain distilled white vinegar) in a dropper bottle or in a small cup with a medicine dropper
  • Pie tin
  • Paper towels
  • Steel nail
  • Optional: handheld magnifier
  • Rock samples (in the video: bituminous coal, limestone, conglomerate, coquina, shale, siltstone, sandstone, and dolomite)

Download worksheet and exercises

If your sample fizzed, you’ve got carbonate in your sample, and your sample might be calcite, marble, coquina, or limestone. If the powder fizzed, you’ve probably found dolomite, which is similar to calcite except it also has magnesium, which bonds more tightly than calcium, making the sample less reactive than limestone.

The reaction doesn’t always occur quickly. Sometimes you’ve got to be patient and wait. For example, magnesite has a weak reaction with acid, and if you grind it to a powder and then test, you have to wait half a minute for tiny bubbles to form. Magnifiers are helpful for these smaller, weaker reactions.

A lot of rocks contain small amounts of calcite or other carbonate minerals, so all of these make a fizz even though carbonate is only a small part of the rock. There might be small veins or crystals of carbonate minerals that you can’t even see, yet when you place a drop of acid on them, they bubble up. You can tell these types of rocks from the real thing because you won’t be able to do more than one acid test on them. The second time you try to add a drop of acid, there will be no reaction. The acid test is just one of many tests used, and shouldn’t be the only one that you use to determine your sample’s identification.

Chemically speaking, when you add the acid to the samples, you’re dissolving the calcium in the samples and releasing carbon dioxide gas into the air (these are the bubbles you see during the reaction).

For calcium carbonate and vinegar, the reaction looks like this:

2CH3COOH + CaCO3 → Ca(CH3COO)2 + H2O + CO2

The first term on the left CH3COOH is the acetic acid (vinegar), and the second term CaCO3 is the calcium carbonate. They both combine to give water H2O, carbon dioxide CO2, and calcium acetate Ca(CH3COO)2.

Carbonate minerals that react with acid (either vinegar or hydrochloric acid (HCl) as shown in the video) include aragonite, azurite, calcite, dolomite, magnesite, malachite, rhodochrosite, siderite, smithsonite, strontianite, and witherite. You can increase the reactivity with HCl by warming the HCl solution before using for the acid test.

You can do this experiment in other ways, too! Place a piece of chalk in a cup of vinegar and watch the tiny bubbles form on the chalk. This also works for egg shells, because they also contains calcium.

Do not let kids test their minerals with hydrochloric acid.

(For teachers demonstrating the HCl version of this test: CaCO3 + 2HCl → Ca++ + 2Cl--+ H2O + CO2)

Note: a few rocks, like coquina, oolite, and tufa can produce an extreme reaction with hydrochloric acid because they have a lot of calcite, and/or a lot of pore space that allows for high surface areas (exposing more of the calcium carbonate to the acid). The reaction will be quick, foamy, and vigorous, which is why we only use one drop of acid at a time.

  1. Number and label your samples using the data table.
  2. Use a dropper to take vinegar out of its bottle.
  3. Drop a few drops onto your sample and watch for a reaction. You’re looking for bubbles, both in size and quantity. A few tiny bubbles don’t count. You’re looking for a reaction similar to the baking soda and vinegar reaction you are probably familiar with.
  4. Optional: check with your hand lens while the reaction is taking place.
  5. Record your observations in your data table.
  6. Wipe your samples dry with a clean, damp cloth.
  7. Test the hardness of your sample with the nail and record it in your data table. If the sample is softer than the nail, you’ll see a scratch and a powder left behind. Scratch it a couple of times to dig up more powder, then add a drop of the vinegar to the powder. Record your results. Did you see bubbles on the powder?

Do not let kids test their minerals with hydrochloric acid. (For teachers demonstrating the HCl version of this test: CaCO3 + 2HCl → Ca++ + 2Cl--+ H2O + CO2) Note: a few rocks, like coquina, oolite, and tufa can produce an extreme reaction with hydrochloric acid because they have a lot of calcite, and/or a lot of pore space that allows for high surface areas (exposing more of the calcium carbonate to the acid). The reaction will be quick, foamy, and vigorous, which is why we only use one drop of acid at a time. Exercises

  1. What state(s) of matter is/are present during the chemical reaction of the acid test?
  2. Write the chemical equation that describes the reaction using your own words. For example, to make water, you’d write: oxygen + hydrogen = water. What would you write for the reaction on the rocks?

Lesson 8: Sedimentary, Metamorphic and Igneous Rocks

Clastic rocks come in very different shapes and sizes, but they all have a few characteristics in common. A clast is a grain of sand, gravel, pebble, etc that makes up a rock. Clastic rocks look like they are made up of fragments of other rocks.

Materials

  • Small piece of plate glass
  • Magnifying lens
  • Vinegar
  • Paper towel
  • Shallow dish
  • Rock samples (in the video: bituminous coal, sandstone, siltstone, shale)

Download worksheet and exercises (Note this worksheet also covers content from Lessons 18 & 19)

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.

  1. Number and label your samples with your data table.
  2. Take your hand magnifier and look closely at each sample and record the color information on the data table.
  3. Use a dropper to take vinegar out of its bottle.
  4. 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.
  5. Wipe your samples dry with a clean, damp cloth.
  6. Test the hardness of your sample with the nail and record it in your data table using Mohs’ Hardness Scale.

Exercises

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

Lesson 9: Burning Coal

Bituminous coal (also called black coal) is a soft, black organic sedimentary rock that contains 85% carbon. It’s a lower grade than anthracite coal, which contains 93% carbon. Bituminous coal can either be dull or shiny, whereas anthracite is hard and shiny. Lignite, a lower grade than bituminous, is a crumbly, black type of coal that only contains 72% carbon.
Materials

  • Votive candle
  • Paperclip
  • Hammer (if your piece of coal is large)
  • Pliers (to bend paperclip)
  • Lighter with adult help
  • Cup of water
  • Rock samples (in the video: bituminous coal, anthracite coal)

Download worksheet and exercises

Coal comes in two main forms: bituminous and anthracite. Bituminous coal is the stuff used to generate energy, whether electricity, heated water, or as a product in other substances. It’s more abundant than anthracite, which is the purer version of coal. Anthracite burns hotter and cleaner, but it’s more scarce. Coal also exists in two other forms as peat, which used to serve as fuel for heating homes as well as lignite, which is more pure than peat but not quite as pure as bituminous.

Coal is one of the two kinds of rocks that are not made from minerals (amber is the other).

Today’s lab lets you burn coal to identify the byproducts of combustion. When coal is burned, it releases volatile compounds that are hazardous to your health, including methane, hydrogen, carbon monoxide, carbon dioxide, nitrogen, and volatile hydrocarbons, but the chemical reaction leaves behind a purer form of carbon than found in the coal itself. So make sure to do this experiment outside!

  1. Move your experiment outside. Do not do this indoors! Fumes generated must be properly ventilated.
  2. Open up and bend the paperclip into a shape that will allow you to hold the coal without it falling off the end. Use pliers to bend the paperclip.
  3. Set a small piece (about the size of a pea) of bituminous coal at the end of the paperclip.
  4. Put on your goggles. NO EXCEPTIONS!
  5. Have an adult light your candle.
  6. Place the coal piece at the top of the flame for the most intense heat.
  7. Look for brown to black smoke to come from the coal. Record your observations in your data table.
  8. When you’re done, place the entire piece of coal in your cup of water.

Optional: If you’ve got a test tube and stand, you can do the following experiment:

  1. Put on your goggles, and pick up the test tube with the test tube holder.
  2. Place a small piece of bituminous coal in the test tube (about the size of a pea).
  3. Place the tube at an angle in a proper holder.
  4. Turn on the heat source, and wave it near the bottom of the test tube for a few minutes, until you notice any slight changes.
  5. As your coal sample heats up, look for bubbles or gas, which is coal gas, one of the first of three things produced by coal. The coal gas was captured and used as fuel in household lamps and streetlights before electricity was available.
  6. As you continue to heat the sample, look for brown stuff along the sides of the tube called coal tar, which is used in dyes, aspirin, textiles, pesticides, and more.
  7. As your sample continues to burn, notice if there are any gray-black solids in the bottom. This will look a lot like ash, but it’s called coke and it’s used to purify metals in a chemical process.

Exercises

  1. What are the three products that coal generates?
  2. Name four types of coal.
  3. What are two things we use coal for?
  4. What type of coal is the most pure?
  5. What is the dominant element in coal?
  6. What are three alternatives to generating energy, instead of using coal?

Lesson 10: Tenacity

Tenacity is a measure of how resistive a mineral is to breaking, bending, or being crushed. When you exceed that limit, fracture is how the mineral breaks once the tenacity (or tenacious) limit has been exceeded.
Materials

  • Hammer (if your piece of coal is large)
  • Rock samples (in the video: copper, mica, selenite, sulfur)

Download worksheet and exercises

Tenacity is a measure of how a mineral behaves when under stress, like being crushed, bent, torn, or hammered. Minerals will react differently to each type of stress. Minerals can have more than one type of tenacity, since it’s possible for a mineral to have different (or several at the same time) reactions to the stress. Here’s a way to classify their response to stress:

  • Brittle: The sample crumbles or turns into a powder. Most minerals are brittle, like quartz.
  • Sectile: These minerals can be separated with a knife, like wax, like gypsum.
  • Malleable: When you hammer the mineral and it flattens instead of breaks, it’s malleable like silver and copper.
  • Ductile: A mineral that can be stretched into a wire is called ductile. All true metals are ductile, like copper and gold.
  • Flexible-Inelastic: When you bend a mineral and release it, it stays in the new shape. It was flexible enough to bend, but it didn’t snap back into its original shape when released, like copper.
  • Flexible-Elastic: When you bend a mineral and release it, it springs back into its original shape. Minerals that are flexible-elastic are fibrous, like chrysotile serpentine.
  1. Label and number each of your samples with your data table.
  2. Use a hammer and try to break the copper sample. Make sure you do this on a hard surface (like the concrete) so you don’t damage your floor or table!
  3. To test for brittleness, like for sulfur, do a scratch test to see if it leaves a fine powder. Use your streak plate if you think your specimen has a hardness of less than 7.
  4. For sectile tenacity, like with mica, carefully insert a knife into the mineral to see if it goes through. If the knife can penetrate through the sample (be careful with this!), then it’s sectile.
  5. To check for flexibility, like mica and selenite, use only slight pressure so you don’t break your sample. Notice if the sample springs back or retains its new shape when released.
  6. Complete the data table with your observations.

Exercises

  1. What are four different types of tenacity?
  2. How is elastic different from inelastic tenacity?
  3. How many types of tenacity can a mineral have?
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