1. Rocks and Minerals

2. What is a Mineral? If you were going out to find minerals, where would you look? You can find minerals in your own home- in the salt shaker and in your pencil. Metal pots, glassware, and ceramic dishes are products made from minerals. Minerals and products made from minerals surround you.

3. Minerals Minerals are naturally occurring, inorganic solids that have a definite chemical composition and crystal shape. Inorganic means they usually are not formed from living things such as plants and animals. X-ray patterns of a mineral how an orderly arrangement of the atoms. This orderly arrangement is the crystal shape often seen in minerals. The chemical composition and arrangement of atoms in the crystals is unique to each mineral.

4. Each mineral has unique characteristics you can use to identify it. So far, 4,000 minerals have been identified. Rocks are usually made of two or more minerals.

5. How do minerals form? Minerals form in several ways. One way is from melted rock material inside Earth called magma. As magma cools, atoms combine in orderly patterns to form minerals. Minerals can also form from magma that reaches the Earth’s surface called lava. Evaporation can form minerals. Ex: salt crystals appear when seawater evaporates.

6. A process called precipitation can form minerals. Water can only hold so much dissolved material. Any extra separates and falls out as a solid. Large areas of the ocean floor are covered with manganese nodules that formed this way. These metallic spheres average 25 centimeters in diameter. They crystallize directly from seawater containing metal atoms.

7. Formation Sometimes you can tell how a mineral forms by how it looks. Large mineral grains that fit together like a puzzle seem to show up in rocks formed from slow cooling magma. Large, perfectly formed minerals formed where the mineral had plenty of space in which to grow. This is a sign that it may have formed in open pockets within the rock.

8. Fluorite grew this way from a solution rich in dissolved minerals. To figure how a mineral was formed, you have to look at the size of the mineral crystal and how the crystals fit together.

9. Properties of Minerals Crystals- All minerals have an orderly pattern of atoms. The atoms making up a mineral are arranged in a repeating pattern. A crystal is a solid in which the atoms are arranged in a definite pattern that is repeated over and over again. Sometimes crystals have a smooth surface called crystal faces.

10. The mineral pyrite forms crystals with six crystal faces. Crystal structure of pyrite.

11. Another clue to a mineral’s identity is the way it breaks. Minerals that break into pieces with smooth, regular planes that reflect light are said to have cleavage. An example of a mineral with cleavage is mica. It shows cleavage by splitting into thin sheets.

12. Some minerals break into pieces with jagged or rough edges. These pieces are not in neat slices but instead look like chunks torn from a larger piece. Materials that break this way have what is called fracture. Examples of minerals that breaks this way are quartz and flint.

13. Sometimes a mineral’s color can help you figure out what it is. Color can also fool you. The common mineral pyrite has a shiny, gold color similar to real gold. Many prospectors during the Gold Rush were fooled by it and it became known as “fool’s gold.” Calcite can form in a variety of colors caused by impurities. Calcite Sulfur Fluorite

14. Scraping a mineral sample across an unglazed, white tile, called a streak plate, produces a streak of color. The streak is not necessarily the same color as the mineral itself. The streak of powdered mineral is more useful for identification than the mineral’s color.

15. Another property of a mineral is luster. Luster describes how light reflects from a mineral’s surface. If it shines like a metal, the mineral has a metallic luster. Nonmetallic minerals can be described as having pearly, glassy, dull, greasy, or earthy luster.

16. Some minerals are harder than others. Some minerals, like talc, are so soft that they can be scratched with a fingernail. Others, like diamond, are so hard that they can be used to cut almost anything else.

17. In 1822, and Austrian geologist named Friedrich Moh noticed hardness as a property of minerals. He developed a way to classify minerals by their hardness. The Moh’s scale classifies minerals from 1-10 with 1 being the softest and 10 being the hardest.

18. Some minerals are heavier for their size than other. Specific gravity compares the weight of a mineral with the weight of an equal volume of water. Pyrite is about five times heavier than water. You could sense this by holding each one in your hand. Some minerals have other unusual properties that can help identify them. Magnetite will attract a magnet. Calcite will fizz when it comes into contact with an acid like HCl. When looking through calcite, you will see a double image. Halite has a salty taste.

20. Common Minerals Rocks that make up mountains are made of minerals. Only a small number of minerals make up most rocks. These minerals are called rock- forming minerals. Some minerals are rare and are used as gems or they are ore minerals, which are sources of valuable metals.

21. Rock-Forming Minerals Most of the rock-forming minerals are silicates, which contain the elements silicon and oxygen. Quartz is pure silica. More than half the minerals in Earth’s crust are types of a silicate mineral called feldspar. Other important rock- forming minerals are carbonates which contain carbon and oxygen. The carbonate mineral calcite make up most of the common rock limestone.

23. Other common minerals can be found in rocks that formed at the bottom of ancient, evaporating seas. Rocks made up of the mineral gypsum are abundant in many places, and rock salt (halite) underlies large parts of the Midwest. The rock forming minerals include feldspar, quartz, olivine, mica, clay minerals, amphibole, pyroxene, and carbonates. These minerals together contain the eight most common elements in Earth’s crust which are oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium.

24. Gems Gems are minerals that are rare and can be cut and polished, giving them a beautiful appearance. To be gem quality, most minerals must be clear with few or no blemishes or cracks. It must have a beautiful luster or color. Few minerals meet these standards and that is why the ones that do are rare and valuable. One reason gems are rare is that they are formed under special conditions.

25. Making of Gems Diamonds are formed from the element carbon. Diamonds form deep in Earth’s mantle. It takes a certain kind of volcanic eruption to bring diamonds close to the Earth’s surface. This kind of eruption forces magma from the mantle towards the surface of the Earth at high speeds, bringing the diamonds with it. This type of magma is called kimberlite. Deposits are found in the necks of some ancient volcanoes.

27. Precious Gemstones Semi-precious Gemstones

28. Ores A mineral is called an ore if it contains enough of a useful substance that can be sold for a profit. Many of the metals that humans use come from ores. Iron used to make steel come from hematite, lead for batteries come from galena, and magnesium used in vitamins comes from dolomite. Ores must be extracted from the Earth in a process called mining.

30. Ore Processing After an ore has been mined, it must be processed to extract the desired mineral or element. Copper smelting plants melt the ore and then separates and removes most of the unwanted materials. After smelting, copper can be refined, which means purified. It is then processed into many materials that you use everyday.

31. Examples of useful copper products include sheet- metal products, electrical wiring in cars and homes, and just about anything electronic.

32. Igneous Rocks Igneous rocks form when melted rock material (magma) from inside the Earth cool. When melted rock cools inside the Earth it forms intrusive igneous rocks. When melted rock cools on the surface of the Earth, it makes extrusive igneous rock. The chemicals in the melted rock determine the color of the rock. If it contains a lot of silica, the rock will be light in color. Light colored igneous rocks are called granitic.

33. If the rock contains a lot of iron, magnesium, or calcium, it will be dark in color. This dark colored rock is called basaltic. Intrusive igneous rocks are often granitic, and extrusive igneous rock are usually basaltic.

34. Extrusive Igneous Rock When the melted rock reaches the surface of the Earth, it is called lava. Lava cools quickly before large crystals have time to form. This is why extrusive igneous rocks usually have a smooth, sometimes glassy appearance. Extrusive igneous rocks form in two ways. Volcanoes erupt and shoot out lava or large fissures (large cracks) open up and lava oozes out onto the ground or into the water. This is called a lava flow.

36. Intrusive Igneous Rock Some melted rock material never reaches the Earth’s surface. The underground melted rock is called magma. Intrusive igneous rock form when a large amount of magma is forced upward towards the surface but never reaches the surface. This hot mass of rock material sits under the surface and cools slowly over millions of years until it is solid.

37. The cooling is so slow that the minerals in the magma have time to form large crystals that are easy to see. Granite Quartz GabbroPegmatite

38. Sedimentary Rocks Pieces of broken rock, shell, mineral grains, and other materials make up what is called sediments. Sediments can collect in layers to form rocks. These rocks are called sedimentary rocks. Rivers, oceans waves, mudslides, and glaciers can carry sediments. When sediment is dropped, or deposited, by wind, ice, gravity, or water, it collects in layers. Most sedimentary rocks take thousands to millions of years to form.

39. Detrital Sedimentary Rocks Detrital or clastic sedimentary rock are made of grains of minerals or other rocks that have moved and been deposited in layers by water, ice, gravity, or wind. Other minerals dissolved in water act to cement these particles together. The weight of the sediment above them squeeze or compacts the layers into rock.

40. To identify a detrital sedimentary rock, you use the size of the grains that make up the rock. Small sized grains feel slippery when wet and make up a rock called shale. Silt-sized grains are slightly larger. These make up the rougher-feeling siltstone. Sandstone is made of even larger sand-sized grains. Pebbles mixed and cemented together with other sediment make up rocks called conglomerates.

41. Shale Siltstone SandstoneConglomerate

42. Chemical Sedimentary Rocks Some sedimentary rocks form when seawater, loaded with dissolved minerals, evaporates. As the water evaporates, layers of minerals are left behind. Chemical rocks form this way from evaporation or chemical processes. Examples of chemical sedimentary rocks include halite and gypsum. Stalactites and stalagmites are also formed this way.

43. Gypsum Halite

44. Organic Sedimentary Rock Organic rocks form over millions of years. Living matter dies, piles up, and then is compressed into rock. If the rock is formed from layers of plants piled up on top of one another, it is called coal. Rocks also form in the ocean and are classified as limestone. Chalk and other types of fossiliferous limestone are made from fossils of millions of tiny organisms. A fossil is the remains or trace of a once-living plant or animal