Text 6. Mineralogy

Mineralogy is the identification of minerals and the study of their properties, origin, and classification. The properties of minerals are studied under the convenient subdivisions of chemical mineralogy, physical mineralogy, and crystallography. The properties and classification of individual minerals, their localities and modes of occurrence, and their uses are studied under descriptive mineralogy. Identification according to chemical, physical, and crystallographic properties is called determinative mineralogy.

Chemical mineralogy. Chemical composition is the most important property for identifying minerals and distinguishing them from one another. Mineral analysis is carried out according to standard qualitative and quantitative methods of chemical analysis. Minerals are classified on the basis of chemical composition and crystal symmetry. The chemical constituents of minerals may also be determined by electron-beam microprobe analysis.

The various classes of chemical compounds that include a majority of minerals are as follows: (1) elements, such as gold, graphite, diamond, and sulfur, that occur in the native state, that is, in an uncombined form; (2) sulfides, which are minerals composed of various metals combined with sulfur. Many important ore minerals, such as galena and sphalerite, are in this class; (3) sulfo salts, minerals composed of lead, copper, or silver in combination with sulfur and one or more of the following: antimony, arsenic, and bismuth; (4) oxides, minerals composed of a metal in combination with oxygen, such as hematite. Mineral oxides that contain water, such as diaspore, or the hydroxyl (OH) group, such as bog iron ore, FeO(OH), also belong to this group; (5) halides, composed of metals in combination with chlorine, fluorine, bromine, or iodine; halite, NaCl, is the most common mineral of this class; (6) carbonates, minerals such as calcite, containing a carbonate group; (7) phosphates, minerals such as apatite, Ca5(F,Cl)(PO4)3, that contain a phosphate group; (8) sulfates, minerals such as barite, BaSO4, containing a sulfate group; and (9) silicates, the largest class of minerals, containing various elements in combination with silicon and oxygen, often with complex chemical structure, and minerals composed solely of silicon and oxygen (silica). The silicates include the minerals comprising the feldspar, mica, pyroxene, quartz, and zeolite and amphibole families.

Physical mineralogy. The physical properties of minerals are important aids in identifying and characterizing them. Most of the physical properties can be recognized at sight or determined by simple tests. The most important properties include powder (streak), color, cleavage, fracture, hardness, luster, specific gravity, and fluorescence or phosphorescence.

Crystallography.  The majority of minerals occur in crystal form when conditions of formation are favorable. Crystallography is the study of the growth, shape, and geometric character of crystals. The arrangement of atoms within a crystal is determined by X-ray diffraction analysis. Crystal chemistry is the study of the relationship of chemical composition, arrangement of atoms, and the binding forces among atoms. This relationship determines minerals’ chemical and physical properties. Crystals are grouped into six main classes of symmetry: isometric, hexagonal, tetragonal, orthorhombic, monoclinic, and triclinic.

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NOTES:

• antimony - сурьма;

• streak – прожилок, прослойка, жила, черта минерала.