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Unformatted text preview: LABORATORY # 1A – ROCK-FORMING MINERALS During this laboratory, you will be studying the properties of minerals and how these are utilized in the interpretation of the Earth's history. A mineral is a naturally-occurring, inorganic, homogeneous, crystalline solid. Therefore, man-made materials, such as synthetic gemstones or plastics, would not be considered minerals. Organic substances are also typically excluded from mineral classification and so natural resins, petroleum and natural gas are usually not considered minerals. A mineral must also have homogeneous chemical and physical characteristics. The chemical formula and physical properties of many specimens of the same mineral should be relatively constant and therefore it is possible to distinguish one mineral from another by physical or chemical means. Finally, a mineral has a definite crystal structure and occurs in a solid state. Amorphous substances, in which a crystal structure is lacking, are excluded from the mineral classification However, mineral-like substances that lack a crystalline structure, such as opal, are termed mineraloids and these substances are often studied by the mineralogist. Mineral types may be differentiated from one another on the basis of their chemical characteristics or physical properties. In this laboratory we will be using the physical properties of luster, color, streak, hardness, cleavage, fracture, crystal habit, specific gravity, and a number of special properties to differentiate one mineral from another. Luster is the appearance of a mineral in reflected light. Luster may be divided into metallic or nonmetallic types. A metallic luster has the appearance of a metal object, such as a coin. Many of the economic minerals, those minerals that are utilized by man, have metallic or submetallic lusters. Many of these metallic minerals belong to the oxide or sulfide chemical groups. Nonmetallic lusters include a number of different types such as vitreous, resinous, waxy, pearly, silky and earthy or dull. Vitreous lusters appear glassy. Many silicate minerals have vitreous lusters. This type of luster will be encountered frequently when studying rock-forming minerals. A resinous luster looks like hardened tree "sap". This luster is relatively rare and is best characterized by the zinc-bearing mineral sphalerite. Another luster, termed waxy , has the appearance of beeswax. The mineral chalcedony can often be distinguished from most other silicates on the basis of it's waxy luster. A pearly luster resembles the irridescent "mother of pearl" layer on a seashell and a silky luster resembles a bundle of silk fibers. Some varieties of gypsum have a pearly luster, whereas others are silky or vitreous. A very common type of luster is earthy or dull . This is a "dirt"-like luster and is found in a wide variety of rock-forming minerals....
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This note was uploaded on 01/16/2012 for the course GEOL 106 taught by Professor Dr.phillipmurphy during the Fall '10 term at Tarleton.
- Fall '10