1. What Are Minerals?

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Minerals stronger and more directional than pure metallic bonding, resulting in crystals of lower symmetry. 5.1.3. Non-metals The native non-metals diamond, graphite, and sulphur are structurally distinct from the metals and semimetals. The structure of sulphur, usually orthorhombic in form, may contain limited solid solution by selenium. The polymorphs of carbon, graphite and diamond display dissimilar structures, resulting in their differences in hardness and specific gravity. In diamond, each carbon atom is bonded covalently in a tetrahedral arrangement, producing a strongly bonded and exceedingly close-knit but not closest-packed structure. The carbon atoms of graphite, however, are arranged in six-member rings in which each atom is surrounded by three close-by neighbours located at the vertices of an equilateral triangle. The rings are linked to form sheets that are separated by a distance exceeding one atomic diameter. Van der Waals forces act perpendicular to the sheets, offering a weak bond, which, in combination with the wide spacing, leads to perfect basal cleavage and easy gliding along the sheets. 5.2. Class 2: Sulphides This important class includes most of the ore minerals. The similar but rarer sulpharsenides are grouped here as well. Sulphide minerals consist of one or more metals combined with sulphur; sulpharsenides contain arsenic replacing some of the sulphur. Sulphides are generally opaque and exhibit distinguishing colours and streaks. (Streak is the colour of a mineral’s powder.) The no opaque varieties (cinnabar, realgar, and orpiment) possess high refractive indices, transmitting light only on the thin edges of a specimen. Few broad generalizations can be made about the structures of sulphides, although these minerals can be classified into small groups according to similarities in structure. Ionic and covalent bonding are found in many sulphides, while metallic bonding is apparent in others as evidenced by their metal properties. The simplest and most symmetric sulphide structure is based on the architecture of the sodium chloride structure. 91
5.3. Class 3: Sulphosalts Minerals There are approximately 100 species constituting the rather large and very diverse sulphosalt class of minerals. The sulphosalts differ notably from the sulphides and sulpharsenides with regard to the role of semimetals, such as arsenic (As) and antimony (Sb), in their structures. In the sulpharsenides, the semimetals substitute for some of the sulphur in the structure, while in the sulphosalts they are found instead in the metal site. 5.4. Class 4: Oxides and hydroxides This class consists of oxygen-bearing minerals; the oxides combine oxygen with one or more metals, while the hydroxides are characterized by hydroxyl (OH) - groups. The oxides are further divided into two main types: simple and multiple. Simple oxides contain a single metal combined with oxygen in one of several possible metal: oxygen ratios (X:O): XO, X2O, X2O3, etc. Ice, H2O, is a simple oxide of the X2O type that incorporates hydrogen as the cation. Although SiO2 (quartz and its polymorphs) is the most commonly occurring oxide, it is discussed below in the section on silicates because its structure more closely resembles that of other silicon-oxygen compounds. Two nonequivalent metal sites (X and Y) characterize multiple oxides, which have the form XY2O4. Unlike the minerals of the sulphide class, which exhibit ionic, covalent, and metallic bonding, oxide minerals generally display strong ionic bonding. They are relatively hard, dense, and refractory. These minerals generally occur in small amounts in igneous and metamorphic rocks and also as preexisting grains in sedimentary rocks. 5.5. Class 5: Halides Members of this class are distinguished by the large-sized anions of the halogens chlorine, bromine, iodine, and fluorine. The ions carry a charge of negative one and easily become distorted in the presence of strongly charged bodies. When associated with rather large, weakly polarizing cations of low charge, such as those of the alkali metals, both anions and cations take the form of nearly perfect spheres. Structures composed of these spheres exhibit the highest possible symmetry. 92
Page 1 and 2: 1. What are minerals? MINERALS Mine
Page 3 and 4: Minerals 1. Talc 2. Gypsum ________
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Page 9: Minerals calcium (Ca 2+ ) and magne

1. What Are Minerals?

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