***Hardness Minerals***

1. TALC, hardness of 1

Hydrated magnesium silicate. This mineral is usually found in metamorphosed oceanic crust. It is so soft that your fingernail will scratch it. Economic use: Ground talc is often used as baby powder. [Web – Put talc rough into Google to see talc used for carving.] Our specimens are from Montana , USA .

2. GYPSUM, hardness of 2

Hydrated calcium sulfate: A very common mineral that precipitates as seawater evaporates. Economic uses: Heated in a kiln to make Plaster of Paris, then formed into wallboard. [Web – Put naica gypsum into Google to see the huge gypsum crystals from Mexico .] These gypsum plates come from New Mexico , USA .

3. CALCITE, hardness of 3

Calcium carbonate: A very common mineral that typically is precipitated by organisms like clams which use it to make their skeletons. When large amounts of these biological products accumulate and get cemented together, the rock is called limestone. Calcite may be dissolved and re-precipitated by hot ground water as large and beautiful crystals. [Web – Put calcite collectors into Google to see the varieties.] These are cleavage fragments. Economic uses: Calcite in the form of limestone is a component of Portland cement, added to cement to make concrete, and as road gravel.

4. FLUORITE, hardness of 4

Calcium fluoride: Typically found in beautiful crystals in hydrothermal deposits (200 degrees C and 2000 PSI) along with metallic ore minerals. Economic uses: Ancient peoples discovered that fluorite (“flowing stone”) would make many ore minerals melt more easily and huge amounts are used for this purpose by the steel industry. It is also a source for fluorine (as in fluoride in Crest toothpaste). This mineral shows four directions of cleavage. [Web – Put fluorite crystals New Hampshire , USA . into Google to see the range of colors.] These pieces are from

5. APATITE, hardness of 5

Calcium phosphate with some fluorine: Apatite comes from both organic and inorganic sources. Many living creatures (like sharks) make their skeletons and teeth out of hydrated calcium phosphate. Economic use: Their accumulated remains are mined for fertilizer. Inorganic apatite is found in igneous rocks. [Web – Put apatite crystals into Google to see the range of colors.] These crystals are from Mexico .

6. MICROCLINE, hardness of 6

Potassium aluminum silicate: Microcline is one of a family of minerals called feldspars. They are found in igneous rocks and weather to clay minerals. Note that there are two directions of cleavage at nearly right angles (micro-cline = little angle) to each other. [Web – Put feldspar moonstones into Google to see optical effects.] I do not know where these cleavage pieces are from. Economic use: Glass is made from a mix of quartz and feldspar.

7. QUARTZ, hardness 7

Silicon dioxide: Quartz is the most common mineral on the continents of the earth. Sand is primarily quartz that has eroded from somewhere else, like granites, and has been concentrated by rivers. When minerals cement the sand together, the rock is called sandstone. Quartz can be recognized by its hardness (it will scratch glass) and its lack of cleavage. Broken quartz looks just like broken glass, and is just as sharp. It grows in hexagonal crystals with striations on the sides. Many common forms of quartz (agate, chalcedony, flint, chert, jasper) are made of tiny crystals, the result of rapid crystallization. [Web – Put quartz varieties into Google]. These crystals are from Arkansas , USA . Economic uses: Glass making, filters, and as a component in cement.

8. TOPAZ, hardness 8

Aluminum fluohydroxysilicate: When nicely colored (blue, yellow, pink) and transparent, topaz is a gemstone. Topaz is found in pegmatite veins associated with granites. A pegmatite is the last material to crystallize as a large igneous body cools. Pegmatites frequently contain rare and beautiful minerals like topaz. Our specimens are rounded, water-worn pebbles collected from a stream in Brazil , so they do often not show crystal faces. Topaz has a single direction of weakness, called a cleavage plane, which shows up if a pebble is broken. [Web – Put Brazil topaz crystals into Google.] Economic uses: As a gemstone.

9. CORUNDUM, hardness 9

Aluminum oxide: Corundum is found in silica-deficient, high temperature metamorphic rocks or in aluminum-rich igneous rocks. If silica is present, corundum will not form because aluminum silicates are much more stable. The diagnostic test for corundum is its hardness. You will find it harder than anything in this box, harder than any mineral but diamond. Minor impurities can color corundum red (ruby) or blue (sapphire). [Web – Put mineral corundum into Google and see the range of colors for corundum.] These corundum crystals are from India . Economic uses: As a gemstone and abrasive.

***Minerals***

10. GARNET (grossular) – Mexico

Calcium aluminum silicate: This garnet is light colored because it is does not contain iron or manganese. Note the shape of this crystal. It has 12 sides and is called a rhombic dodecahedron because each of the faces is a rhomb. [Web – Put Rhombic Dodecahedron into Google and see some great pictures of this crystal shape.] Recognizing this crystal shape is key for identifying garnets. Garnets come in a wide range of colors. [Web – Put garnet colors into Google.] This mineral will scratch glass. Economic uses: A common abrasive in sandpaper and as a gemstone.

11. CALCITE – location unknown

Calcium carbonate. This specimen is for breaking. Look at the shape of the cleavage fragment and see that it has three directions of cleavage (planes of fracture), none of which is perpendicular. Gently tap this cleavage fragment with a hammer until it breaks. Note that all the fragments have the same shape as the original. The fracture planes and the angles are diagnostic for this mineral. [Web – Put crystal cleavage into Google to see sites that discuss this important feature.] Save the fragments to show again.

12. PYRITE, known as "fool's gold," – from the silver mines of Peru .

Iron sulfide: Diagnostic properties are its brassy gold color, its brittleness, and when present, its cubic crystals. Once a minor iron ore, most pyrite is mined today for its trace content of precious metals like gold. [Web – Put pyrite specimens into Google.] Pyrite can grow in cubes or pyritohedrons (12-sided crystal where the faces are pentagons). [Web – Put pyritohedron into Google to see a description of the crystal shape.] Pyrite is a striking example of metallic luster: It is shiny and opaque because it reflects light. Economic uses: Pyrite commonly contains gold and is also an ore of sulfur.

13. BARITE – cleavage fragment from Hatch, NM.

Barium sulfate: Barite is a white mineral. Try a “heft” test and note that barite (density of 4.3) has a much greater specific gravity than quartz (density of 2.9) or calcite. Economic uses: Barite is commonly used in drilling mud to make it much heavier than water. A “barium milkshake” is a suspension of barite and clay that is given to patients to make their intestinal track visible on X-rays. [Web – Put barite uses into Google to see industrial uses.]

14. HEMATITE – massive hematite from Arizona .

Iron oxide: This specimen has a striking “specular” (like a mirror) luster. Economic use: This mineral is quite important as an ore of iron. It is produced in blast furnaces where carbon from coke (from coal) is mixed with hematite and burned in a blast of air. The partial combustion of the carbon produces carbon monoxide (CO) which captures oxygen from the iron oxide to produce metallic iron. Finely divided hematite is red in color. Though these specimens are black, they will produce a red streak on the back of the ceramic plate. [Web – Put hematite mineral into Google to see mineral varieties.]

15. QUARTZ – milky quartz – Texas - warning SHARP Edges

Silicon dioxide: These are broken pieces of quartz and show no crystal faces. These also show no cleavage because quartz does not break along flat planes; instead, it breaks like glass (“conchoidal” or shell-shaped fracture). The color looks milky because the quartz contains tiny bubbles of the water from which it crystallized. [Web – Put quartz fluid inclusions into Google and click on images to see photomicrographs of the bubbles.] Economic uses: Glass making, filters, and as a component in cement.

16. AZURITE and MALACHITE – Arizona

Hydrous copper carbonate: These minerals are very similar in composition but are very different in color. Azurite is the blue mineral, and it is an inexpensive paint pigment. However, it has a problem in that it gradually alters to the green mineral—malachite—in a humid environment like Houston . Copper is easily corroded to green and blue minerals. Try this experiment. Take a copper penny minted before 1982 (these are all copper rather than the more recent copper plated zinc ones) and wrap it in a paper towel that is moistened with sodium chloride (common salt) solution (about a teaspoon of salt per cup of water). Seal it wet in a jar and leave it a week and you will see green copper chloride corrosion. [Web – Put malachite azurite bisbee Arizona into Google to see bigger specimens.] Economic uses: These two minerals are important sources of copper and as cheap paint pigments.

28. MICA – New Hampshire

Potassium aluminum silicate: The atoms in the mica structure stack up in planes and that is a zone of weakness which caused the mineral to break or cleave in that direction. You can see this by peeling a sheet of the mica off a crystal face.

***Rocks***

These are used in a discussion of the rock cycle.

51. DIRT – Houston , Texas

This is soil from my backyard. A gardener would call it gumbo and a homebuilder would not like it because it is swelling clay. Try the experiment of putting just one drop of water on a lump the size of a pea, and you will see the clay ball swell up when it gets wet. A gardener would dislike this soil because it has a sticky texture. This swelling causes foundations to break and streets to crack. Mix some up in water and you will see that it takes hours for the mud to settle to the bottom of the container indicating that the grain size is very fine. Good soil such as that used in a flowerpot is much easier to work. [Web – Put soil profile into Google.]

17. SHALE – Texas

Shale is a sedimentary rock made up of very small clay and silt particles. [Web – Put shale photomicrograph into Google and see the fine structure in shale.] Economic use: Cement companies make Portland cement by roasting limestone and shale in a huge rotary kiln.

18. SLATE – Maine

Heat and pressure will convert (metamorphose) shale into slate. The metamorphism creates mica flakes perpendicular to the pressure, and the slate splits easily along the mica. A common use for slate is flooring. See slate uses to find other uses. Economic use: Roofing and floor tiles are important uses.

22. GARNET SCHIST – North Carolina .

More heat and pressure will convert (metamorphose) slate into garnet schist. The mica has grown to be quite visible, and some of the iron minerals are now garnet. Look closely and see that the garnet has the same dodecahedral shape as #10. [Web – Put metamorphic rock garnet schist into Google.] Economic use: Garnet schist is mined for the garnet.

19. LIMESTONE – Texas

Limestone is a sedimentary rock that is primarily composed of calcium carbonate. Frequently the calcium carbonate is the skeletons of microscopic animals. This rock will fizz in 5% hydrochloric acid. [Web – Put limestone photomicrograph into Google and see the fine structure of limestone.] Economic uses: Calcite in the form of limestone is a component of Portland cement, it is added to cement to make concrete, and it is used as road gravel.

20. MARBLE – Georgia

Heat and pressure will convert (metamorphose) limestone into marble. Marble is commonly used for flooring and as external panels for buildings. [Web – Put metamorphic rocks marble into Google for more info.] Economic uses: Marble is used as floor and wall tiles. It is also carved into statues which range in size from those you can hold in your hand to whole mountains ( Stone Mt. , Georgia ).

50. SAND – unknown location

This is pure quartz sand that would be suitable to make into glass. Most sand has too many non-quartz grains in it. [Web – Put sedimentary rock sand into Google.] Economic uses: Glass making, filters, and as a component in cement.

26. SANDSTONE – Arkansas

Sandstone is a sedimentary rock made up of visible grains of mostly quartz sand with a small amount of quartz cement. [Web – Put sandstone photomicrograph into Google and see the fine structure of sandstone.] Economic uses: Sandstone is a popular building material.

21. QUARTZITE – Texas

Heat and pressure will convert (metamorphose) sandstone into quartzite. Quartzite has almost no commercial use. [Web – Put quartzite rock into Google to see examples.]

27.  BASALT – Lahitas, Tx

29. Rhyolite – Lahitas, Texas

25. SCORIA – New Mexico

If basalt lava reaches the surface, it flows like honey and the dissolved gas bubbles out (like the fizz in a soft drink) and the rock has a characteristic porous texture. Iron minerals in the lava can oxidize and color the surface red. [Web – Put igneous rock scoria into Google.] Economic uses: Scoria is used as a low density additive to cement and as a decorative stone.

24. PUMICE – California

This rock floats! Try it. You should store the pumice dry to keep it from gradually adsorbing water and sinking. When the lava is very viscous, it cools into what is essentially foam. [Web – Put igneous rock pumice into Google.] Economic use: As an abrasive (Lava soap has ground pumice in it).

23. GRANITE – Texas

The pink crystals are microcline feldspar. The gray areas are quartz. The black spots are biotite mica, magnetite, and pyroxenes. The continents float on a granite basement in a sea of basalt. Economic uses: Floor and wall tiles, headstones, and as huge blocks to make breakwaters offshore of Galveston .

***Fossils***

I am including a limited number of fossils so I can introduce some animal adaptation concepts.

47. COAL – Illinois

Coal is a rock made from the compressed cellulose of plants. For coal to be formed, the plants must have been present in great abundance, and they must have been buried in an oxygen-free environment such as a bog, swamp, or lake. This is bituminous coal, which has been subjected to greater temperatures and pressures during burial than the lignite coals of Texas which still look a lot like peat moss. Economic use: Bituminous coal is burned in power plants to make electricity.

55. PETRIFIED WOOD – Bryan , Texas

Silica: Wood petrifies when the wood cells are filled with silica (quartz or opal). The original cell walls are still present and protected from biological attack by the filling. If you were to put the petrified wood into hydrofluoric acid (Dangerouspetrified wood structure into Google.] Economic use: Pretty petrified wood is quite valuable as a decorative object, but ugly petrified wood mostly resides in gardens. and slow), the silica would dissolve revealing the original wood. This is a hardwood; you can see that it is made up of large cells. [Web – Put

100. OAK – modern

This is not a fossil. Compare with #55 by looking at the end grain (biggest face). You will see that oak is a hardwood because it has cells of different sizes.

57. SHARK TEETH – Peace River , Florida .

Calcium phosphate: A modern sand shark lives for about 15 years, and during that time he discards 40,000 teeth. Each tooth is replaced in about three weeks. Florida mines about one billion pounds of phosphate rock for fertilizer each year, and most of that was derived from animal bone. There is a beach at Tampa , Florida that is brown in color because the grains are bone. Sharks have sharp teeth to capture slippery fish or to cut out pieces from their prey. They do not chew. [Web – Put fossil shark teeth into Google.]

58. RAY TEETH – Peace River , Florida

Calcium phosphate: The grinding surface of the ray tooth is the smooth one. One of the surprising things that rays eat is oysters IN the shell. They crush up the whole thing. Rays are not aggressive to humans. [Web – Put fossil ray teeth into Google.]

Discussions you can do with this set of specimens:

***Hardness***

Hardness – Specimens 1 to 9 are listed in order of the Mohs hardness scale. Try an experiment. Scratch one mineral with another and then do it in reverse order. You will find that the lower numbered specimens are softer than those with higher numbers. Go ahead. Scratch some minerals. That is what they are here for. There are some common materials that you can also use for hardness testing: A fingernail has a hardness of 2½, a copper penny (before 1982) is 3, a steel knife is 5, glass is about 5½, and a steel file is 6½. It is much easier to scratch something with a sharp edge. Rub your finger over the scratch line. If you made a scratch on a softer mineral, then you will see a scratch or indentation, but if you tried to scratch a harder mineral, you will likely see a line of the softer mineral smeared on the harder one. Check to see which scratched which.

Safety tips:

If you are scratching glass, put the glass plate on the table; don’t hold it in your hand. Use thick pieces of glass (like a Ward’s scratch plate or a pickle bottle), not thin things like glass slides.

When doing a hardness test with a nail, be careful not to stick yourself or anyone else.

***Mineral Properties***

Minerals are natural, inorganic, solid crystalline compounds. They have fixed chemical compositions and regular crystalline structures. Rocks are mixtures of minerals and may contain substances (like coal) that are not minerals.

Crystal shape – Crystal shape is one of the diagnostic features of minerals. Note that corundum (#9) is hexagonal in shape, as is apatite (#5). Quartz (#6) is different. It is ditrigonal. That means that its shape is two three-sided prisms. Look at the crystal and note that the prism is not made up of six equal-sized faces but of two sets of three equal-sized faces. Can you prove that the crystals in the garnet schist (#22) have the same shape as #10?

Cleavage – Demonstrate that cleavage for calcite (#11) is size independent.

Density – Pick up the barite (#13) in one hand and pick up another specimen of about the same size in the other. Juggle them up and down, and you will notice that the barite is considerably heavier. If you have the equipment, measure the specific gravity of each by weighing the specimen, getting the volume by lowering it on a string into a volumetric cylinder, and determining the density in grams/cm³. Another way to measure specific gravity is to weigh the specimen in the air and then in water. The difference is the volume. The specific gravity, then, is the weight in air divided by the weight loss in water.

Can you support my contention that #15 is quartz even though it looks nothing like #7?

Chemical reactions – Try the copper corrosion experiment as mentioned above with salt and sodium bicarbonate. Check for color differences. Try again with a lemon.

Prove that limestone fizzes with 5% hydrochloric acid. It will not work with vinegar. Obtain an oyster shell and try again.

Streak – Streak is also diagnostic for many minerals. Try it for azurite, hematite, and pyrite. Some streaks are vastly different colors than the bulk mineral.

Pollution – Burn a bit of coal and smell the stink. You are smelling mostly the coal tar and sulfur that distills out of the coal when you burn it. Coal was used for heat in northern cities until the 1960s, and the pollution it caused was amazing. Today coal is used in Texas for power plants, and they can install pollution controls to reduce this problem. [Web – Put china coal smog into Google and click on the images button.] China has the same pollution problem now that the U.S. did in the 1960s, but they have only a limited supply of natural gas to substitute for coal.

***Outline of a Rock Cycle talk***

***Embellish to taste***

The rock cycle explains how igneous, metamorphic, and sedimentary rocks are related to each other. Plate tectonic movement is responsible for recycling rock materials and is the driving force behind the rock cycle.

Start: Depth 5 feet, Time = 2000 years: Suppose you start off by digging a hole in the school lawn. You will find dirt, sand, and maybe a shell. You might also find a fossil elephant. There were elephants (mammoths and mastodons) walking around the area of the school as recently as 10,000 years ago. A pair of elephant tusks (mammoth), were found in Katy 10 years ago, and such fossils are routinely found in the Brazos River . One of the reasons that mammoths are no longer here is that early man may have eaten them! I bet we could feed the whole school on an elephant barbeque.

Dig to 10,000 feet, 2 miles, Time = 1,000,000 years: It getting hotter and the pressure is much higher: dirt to shale; sand to sandstone; shells to limestone. This is just the beginning.

Dig to 100,000 feet, 20 miles, Time = 50,000,000 years: Higher pressure and temperature: shale to slate and then schist; sand to quartzite; limestone to marble.

Dig to 200,000 feet, 40 miles, Time = 100,000,000 years: The rocks are beginning to melt. In the subduction zones under the Pacific coast, things are melting at as little as 20 miles down to a composition similar to granite. If this lava got back to the surface in a volcano, we could expect to see scoria and pumice.

Uplift: Suppose that this part of the Gulf Coast was uplifted and made into mountains like we see in Colorado . The rocks would start to erode. Soft rocks like shale would erode quickly. Since limestone will dissolve in dilute acids like rainwater, it will erode slowly. Hard rocks like granite erode even more slowly. The feldspars break down chemically into clay. The quartz breaks into small grains that are called sand (#50). The clay and sand are washed into rivers, and floods distribute them. Some of these grains could end up on your playground and a kid could start digging a hole. The cycle starts all over.

***Fossils***

A fossil is any trace of previous life—original or mineralized bones, preserved tracks, carbonized leaf remains, and holes left behind when shells dissolve away are all fossils.

Petrify – The petrified wood has been mineralized with quartz. Can you support that claim?

Structure – Look at the cells in the petrified wood (#55) and compare them to #100, a piece of modern oak. In both samples, you should see big and little cells. This is the diagnostic feature for a hardwood.

Animal adaptations – Play paleontologist and consider how different kinds of teeth might affect how an animal lives and its survivability. Sharks have pointy cutting teeth. Cats have pointy teeth. Can cats take a bite out of a mouse, or are they really good at capturing mice? Can sharks chew? Can cats chew?

Rays have crushing teeth and can eat an oyster in the shell. Speculate on what would happen to human teeth if a person tried to eat an oyster in the shell.

Paleoecology – #19 is a limestone that is full of shells. You can see the pearly luster of the broken shell material. The rock is also tan in color because there is clay between the grains of shell material. This rock is a marl (a mix of calcium carbonate and clay). Let’s figure out the environment where this rock was deposited. The shell material is sort of flat, indicating that these shells are bivalves (like oysters or clams). Bivalves are filter feeders. This means that they draw seawater into their shell and capture organic particles from the water. They have to live in water that gets sufficient light so organisms will grow. This means that the water depth has to be less than 100 feet or the sunlight will get absorbed. Typically, bivalves do not crawl or swim, and this means that they would be smothered in areas of high sedimentation such as near the mouth of a river carrying a substantial sediment load (like the Brazos River ). But I just said that the rock is tan from clay, so there must be some input of sediment from a river. The offshore area of Galveston would not be suitable because a bottom dweller would be choked by sand from the Mississippi or other rivers. I would guess that similar conditions could be found on the Florida panhandle where the sediments are mostly carbonate shell debris with a little clay washed in from the Mississippi .

Just by examining the rock, we can tell something about where the animals in it lived.

***Data Experiment***

Checking Results: Divide the people into two groups (A and B). Group A should test the hardness minerals against glass and make a table that shows which is harder. Group B should do the same test against calcite. If a mineral scratches glass, then it should also scratch calcite. Resolve the differences by repeat tests.

Density vs. hardness: Determine the density and hardness of the minerals. Make a graph and see if there is any correlation between hardness and density (there is not).