BASIC MINERALS AND HARDNESS SET 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 numbers are softer than the 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 is hardness of 2 ½, a copper penny (before 1983) is 3, a steel knife is 5, glass is about 5 ½, and a steel file 6 ½. Note: not every mineral is present in every box. We run out and have to substitute other minerals. Check the name and not the number. 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. - Don’t put any mineral in your mouth. - Always wash your hands after handling 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. Ground talc is often used as “baby powder.” 2. GYPSUM, hardness of 2 Hydrated Calcium Sulfate: A very common mineral that precipitates as seawater evaporates. The most common use is for making sheet rock wallboard. 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. 4. FLUORITE, hardness of 4 Calcium Fluoride: Typically found in beautiful crystals in hydrothermal deposits (200 degrees C and 5000 PSI) along with metallic ore minerals. Ancient peoples discovered that fluorite (“flowing stone”) would make many ore minerals melt more easily. This mineral shows 4 directions of cleavage. 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. Their accumulated remains are mined for fertilizer. Inorganic apatite is found in igneous rocks. 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. 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. 8. TOPAZ, hardness 8 - When nicely colored (blue, yellow, pink) and transparent, topaz is a gemstone. Aluminum fluohydroxysilicate: 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, waterworn pebbles collected from a stream in Brazil, so they do not show crystal faces. Topaz has a single direction of weakness, called a cleavage plane, which shows up if a pebble is broken. 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). 10. RHODONITE Manganese silicate: Rhodonite (hardness 5 ½ to 6) is usually found in metamorphic rocks where the heat and pressure create an environment in which the manganese dissolves out of low concentration sources like shale. It can form large masses of beautiful pink stone. You might mistake this mineral for the other common pink mineral, rhodochrosite (hardness 3 ½ to 4), except that rhodonite is much harder. Try a hardness test and see. Rhodonite is a manganese ore and is cut as a semi-precious gemstone. 11. MUSCOVITE Potassium aluminum silicate: Muscovite is found in igneous and metamorphic rocks. The distinguishing characteristic of this mineral is thin, flexible sheets, which can be split off. It has a hardness of 2 to 2½. 12. SIDERITE Iron carbonate: Siderite can be found in sedimentary rocks where it precipitates from seawater as a cement. It also is found in hydrothermal ore veins where it forms in masses with good cleavage like the sample you have. This mineral is harder than calcite (hardness 3) and softer than fluorite (hardness 4). Try it. 13. CALCITE crystals on matrix. Calcium carbonate: Look at your specimen for broken tips on the ends of the crystals. You will see 3 directions of cleavage. Test the hardness to see that this mineral is harder than gypsum and softer than fluorite. 14. AZURITE, blue from Morenci copper mine in Arizona. The green is malachite. Copper carbonate: Azurite and malachite are common copper minerals. A hardness test is difficult because the azurite is a fluffy mass of crystals, which crush when you try a hardness test. Both azurite and malachite are important copper ores. 15. CELESTINE from Lampasas County, Texas. It occurs in cavities in limestone. Strontium sulfate: The red color in fireworks is from strontium. A distinguishing characteristic for this mineral is that it is heavy. You can do a specific gravity test to find that this mineral is 4 times the density of water, but first just try a “heft test”. Take a piece of celestine in one hand and a similar sized piece of calcite or quartz (density of 2.9) in the other and jiggle them. Compare it with siderite. 16. QUARTZ, variety amethyst - from Rio Grande do Sul, Brazil - from cavities in basalt. Silicon dioxide: The purple color is from iron. If you were to wrap this crystal in 10 layers of aluminum foil and heat it for 2 hours at 400 degrees F, it would change color to yellow as the iron changes oxidation state. 17. GYPSUM, “roses” from the Chihuahuan desert of northern Mexico. Calcium sulfate: Gypsum grows in many crystal shapes. This kind grows in sand that is saturated with “hard water” and the calcium sulfate precipitates at the water evaporates. The white deposits on your showerhead are mostly gypsum. You will see that the hardness is the same no matter what shape the crystals are in. 18. 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 and silver. 19. STILBITE occurs in cavities in basalt - from Siberia, Russia, Nova Scotia, Canada and India. Hydrous sodium calcium aluminosilicate. These crystals grow rapidly. Artificial zeolites are used in ion-exchange applications, such as water purifiers. 20. CHRYSOCOLLA is a hydrous copper silicate. From an Arizona copper mine. The blue-green color and the botryoidal growth (lots of tiny, radiating crystals that make a bubbly-looking mass) are typical. Chrysocolla’s nice color and luster make it a semi-precious gemstone. 21. ARAGONITE - twinned crystal from Clarendon, Texas. Calcium carbonate, like calcite, but orthorhombic instead of hexagonal. Unless you have crystals, it is almost impossible to tell calcite from aragonite. Some organisms, like oysters, make aragonite hard parts. 22. GARNET crystal from Malawi in Africa. Aluminosilicate group with extremely variable cation substitution: Garnets occur in many rock types. Though only slightly harder than quartz, garnets are pretty tough. Because they break with a conchoidal fracture (like glass), making lots of little sharp pieces, crushed garnets are used to make sandpaper. When clear and a pretty color (red, orange, green) garnet is faceted as a gemstone. 23. WAVELLITE, green sprays on gray Big Fork chert. From Arkansas. Hydrated aluminum phosphate: a secondary mineral (formed by breaking down phosphates or Al-rich metamorphic rocks). Its bright green, lustrous, radiating, fibrous crystals make it a sought-after specimen but it has little economic importance. 24. VANADINITE, tiny orange to red crystals from Arizona. Lead chloro-vanadinate: a secondary mineral formed by oxidizing lead ores in deserts. (Wash your hands after handling this mineral, even though it is not very soluble in water.) 25. BERYL, small six-sided (hexagonal) crystals from New Hampshire. Beryllium aluminum silicate: Beryl is really hard (H=8), right up there with topaz. Transparent, colorful members of the beryl family (green – emerald, blue – aquamarine, pink – morganite) are prized as gemstones. Beryl is the only important source of the element beryllium. 26. ZOISITE, pink with epidote (green), quartz (white to gray), Baja California. Hydrous calcium alumino-silicate: forms in pegmatites and metamorphic rocks that form when high Ca rocks are subjected to considerable pressure. Crystals radiate from central points, indicating rapid growth. 27. ADAMITE on brown goethite, Mapimi, Durango, Mexico. Zinc arsenate: a secondary mineral formed by oxidizing zinc sulfides and other primary ore minerals. A minor ore of zinc. The yellow varieties are fluorescent and phosphorescent. (Wash your hands after handling this mineral, even though it is not very soluble in water.) 28. KYANITE in QUARTZ from Brazil – Blue blades in a milky quartz matrix. Aluminum silicate: formed from clay that is metamorphosed at high temperatures and pressures. Besides its blue color, the most diagnostic feature is that it is harder when scratched across to the crystals than parallel to them. A knife will make a scratch along the crystals but not across them. 29. HEMIMORPHITE, white to gray crystals in brown to black goethite, Mexico. Hydrous zinc silicate: Naturally colorless, hemimorphite is often colored by minor impurities. Even though it is a silicate, it is pretty soft, H=4.5 to 5. 30. BARITE SAND ROSE or nodule, from Norman, Oklahoma. Barium sulfate: Barite is a white mineral. The red sandstone in which they are found colors these “roses”. A small amount of barium gets “stuck” to the clay minerals that make up a marine mud deposit. When diagenesis transforms that mud into shale, some of the barium is expelled into the ground water. That ground water will be forced through a permeable sandstone layer on its way to the ocean and the barium will encounter sulfate from seawater and be precipitated as barite. 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. Other minerals you may encounter. 26. SPHALERITE, dark brown to black, bright cleavage and dull crystal faces, with yellow chalcopyrite. Zinc sulfide: Sphalerite is the primary ore of zinc. It has good cleavage and a substantial heft. 28. Calcite – cut pieces of calcite onyx, Mexico. Calcium carbonate: This is another form of calcite that is deposited by dripping water in a cave. 29. SMITHSONITE, pinkish bubbly crusts, Mexico. Zinc carbonate: Minor amounts of cobalt color this specimen pink.