No study of mineral resources and mining is complete without attention to the names of specific rocks and minerals, and a knowledge of how these rocks and minerals were formed. Following is a listing of the common rocks and minerals mentioned in the activities. They are presented according to their types, and there is a brief description or definition of each.
The diagram of the rock cycle shown below illustrates the many ways that rocks are changed. Igneous rocks beneath or on the earth's surface are constantly subjected to physical and chemical conditions that change them. As a result of these changes, sedimentary rocks, metamorphic rocks, or new igneous rocks are formed. The continuous changing of rocks from one type to another is called the rock cycle.
Rocks are formed by one of three processes, and they are grouped according to the way they are formedigneous, sedimentary, and metamorphic.
1. Igneous
Igenous rocks are sometimes referred to as "fireformed" rocks. Even though there is no actual fire involved, tremendous heat within the earth's crust produces magma (molten rock). When the magma cools and hardens, either underneath or on the earth's surface, it produces igneous rocks.
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| A coarse-grained, light colored, igneous rock containing quartz, potassium, feldspar, mica, hornblende, and other accessory minerals. |
| A dark gray or greenish igneous rock, consisting chiefly of feldspar and hornblende. |
| Any of a group of fine-grained extrusive igneous rocks having a similar chemical composition to granite, commonly occurring as lava flows, though occasionally as minor intrusions. |
| A volcanic rock composed essentially of andesine, which is a silicate of sodium, calcium, and aluminum. |
| A highly porous igneous glass. Insoluble in water and not attacked by acids. Very light weight and will float on water. |
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| A coarse-grained igneous rock composed of calcic plagioclase, pyroxene, and olivine. |
| Any of several coarse-grained, dark igneous rocks consisting mainly of olivine and other ferromagnesian minerals. |
| The dark gray or black, dense of finegrained, igneous rock that is extruded from a volcano or volcanic vent. |
| Volcanic glass. Usually black, but known also to be red, green, or brown. |
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2. Sedimentary
Sedimentary rocks are formed from sediments or small pieces of rocks, shells, or the remains of plants and animals that over millions of years have settled to the bottom of the ocean or lakes. Sedimentary rocks can also form in environments other than water, for instance, in sand dunes. The sediments become pressed and cemented together to form sedimentary rocks.
| A rock composed of rounded fragments, varying from small pebbles to large boulders, in a cement of hardened clay or the like. |
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| Composed of sharp-cornered bits of fragmented rock, cemented together by sand, clay, or lime. |
| A sedimentary rock composed largely of sand grains, mainly quartz, held together by silica, or lime. |
| A very fine-grained sedimentary stone composed mostly of quartz with some clay. |
| A fine-grained, thinly bedded rock, largely of hardened clay; splits into thin layers. |
| Consists mainly of calcium carbonate, often the organic remains of sea creatures. It is often used as building stone and as a source of lime. |
| Lime or limestone, essentially calcium, carbonate, calcite. |
| Natural sodium chloride occurs in solid form, especially in rocklike masses; halite. |
| A hydrated sulfate of calcium, occurring naturally in sedimentary rocks; chalk. |
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3. Metamorphic
Metamorphic rocks are formed as a result of changes that occur in existing rocks. Conditions such as extreme heat, great pressure, and chemical reactions change existing rocks into new rocks called metamorphic rocks.
| A hard, fine-grained metamorphic rock that cleaves naturally into thin, smooth-surfaced layers. |
| Any of a group of metamorphic rocks containing parallel layers of flaky minerals, as mica or talc, and splitting easily into thin, parallel leaves. |
| A coarse-grained, metamorphic rock resembling granite, consisting of alternating layers of different minerals such as feldspar, quartz, mica, and hornblende, giving it a banded appearance. |
| A very hard metamorphic sandstone cemented with quartz. |
| A hard crystalline or granular metamorphic limestone in varied colors and patterns, capable of taking a high polish. Used in buildings and memorials. |
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Common Rocks
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