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24 specimens, 1 1/4", including six each of the following: rock-forming minerals, igneous, sedimentary and metamorphic rocks. Also includes a study guide. ROCK AND ROCK-FORMING MINERALS ROCK-FORMING MINERALS Minerals are naturally occurring chemical compounds or elements found in the earth's crust and are the building blocks of rocks. Rocks may contain only a single mineral, but usually they contain a mixture of many minerals. 1. Quartz - Silicon dioxide, or quartz, is the most common mineral in the earth's crust.
2. Feldspar var. Microcline - This potassium aluminum silicate is common in pegmatites and in some metamorphic rocks.
3. Mica var. Muscovite - A potassium aluminum silicate that is common in granite pegmatites. Muscovite is also common in metamorphic rocks.
4. Mica var. Biotite - Some granites, schists, and gneisses contain this iron-bearing potassium aluminum silicate.
5. Calcite - Calcium carbonate is the major constituent of limestones and marbles.
6. Hornblende - This complex silicate is common in metamorphic and some igneous rocks.IGNEOUS ROCKS Igneous rocks were once lava or magma, that is, a molten collection of minerals. The rate at which a lava or magma cools and solidifies influences rock texture, making it either fine, medium or coarse grained. 7. Pumice - A light colored volcanic rock of rhyolitic composition; the texture results from bubbles formed by escaping gasses.
8. Obsidian - Very rapid cooling caused this volcanic rock to have its glassy appearance.
9. Basalt - This dark-colored, extrusive rock occurs as large flows, dikes, and sills.
10. Rhyolite - Quartz and microcline are the major components of rhyolite.
11. Andesite - The feldspar phenocrysts present in this light-colored, extrusive rock are the result of relatively slowly cooling lava at shallow depths.
12. Granite - Feldspars and quartz made up the majority of this intrusive rock.METAMORPHIC ROCKS Metamorphic rocks are rocks that have been changed (metamorphosed), by heat, pressure, and/or hydrothermal solutions. All three rock types can be metamorphosed. 13. Mica Schist - This rock is a highly metamorphosed shale. All schists exhibit shistose structure; the generally parallel alignment of micaceous minerals.
14. Slate - The low-grade metamorphism of shale results in slate.
15. Quartzite - The "parent rock" of quartzite is quartz sandstone.
16. Gneiss - All gneisses exhibit gneissic structure, that is, alternating layers of granular minerals and micaceous minerals.
17. Garnet Schist - Shale that undergoes complete recrystallization due to metamorphism often contains high-pressure minerals such as garnet or andalusite.
18. Marble - This rock results when limestones or certain dolomites are metamorphosed.SEDIMENTARY ROCKS Clastic sedimentary rocks are formed from layers of sediment (fragments of older, weathered rock) exposed to pressure. Other sedimentary rocks are of organic or chemical origin. 19. Sandstone - Quartz grains cemented together by silica, calcite or other cementing minerals make up this clastic, sedimentary rock.
20. Shale - Shale is the most abundant of all the sedimentary rocks. It is usually finely bedded and is composed of silt and/or clay size particles.
21. Arkose - This clastic, sedimentary rock is made up primarily of quartz and microcline, with lesser amounts of other minerals.
22. Conglomerate - Rounded pebbles cemented together with finer material make up this clastic, sedimentary rock.
23. Breccia - is composed of re-consolidated angular fragments of gravel and/or sand size particles.
24. Limestone - This sedimentary rock is made up primarily of calcite. Some limestones are chemical in origin, while other are clastic.
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