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Garnet is a common mineral distributed worldwide. It occurs as crystals, in massive and granular forms, and as tumbled pebbles. It can form under a wide variety of geological conditions, but high temperatures are essential for its development. It is of major importance as a rock-making mineral in igneous, metamorphic, and sedimentary rocks. It alters frequently to chlorite, serpentine, and talc. Chemical stability and resistance to weathering permit excellent crystals to be found in alluvial deposits. It is known that inhabitants of the American southwest still recover crystals from the desert sands and ant hills there. Garnet has imperfect cleavage, but it can exhibit an unusual angular fracture. This ability allows it to retain sharp cutting edges. Industry takes advantage of this property and its hardness to produce abrasive papers and cloths that are two to six times more efficient than those of quartz.... (1997) Complete Story
Silicates comprise about a quarter of the known minerals and almost 40% of the common ones. The basic unit of structure of all silicate crystals is the tetrahedron. There are four oxygen atoms, one located at each apex of a regular tetrahedron. A single silicon atom is located at the center of the tetrahedron. This silicon atom has a valence charge of 4, meaning that it is looking to acquire four electrons through sharing with other atoms to complete its outermost energy shell, known as the valence shell..... (2002) Complete Story
The sorosilicate class of minerals is composed of more than seventy minerals. Most are rare, and only a few are used as gemstones or are cut for collectors. The exception, the lovely tanzanite of the zoisite group that forms in the orthorhombic crystal system, was discussed in a previous article. Since the optical and physical properties of the lesser known varieties vary and their use as gemstones is not common.... (2003) Complete Story
Previous articles discussed the polymorph gemstones andalusite, sillimanite, and kyanite of the Al2SiO5 group of the nesosilicates. Topaz and staurolite are the two remaining minerals of this group used as gems. In the nesosilicate structure of orthorhombic topaz, independent.... (2003) Complete Story
With the exception of orthorhombic zoisite (tanzanite and thulite), discussed in the first article on the sorosilicate class of minerals, the members of the epidote group form in the monoclinic crystal system. Allanite, clinozoisite (the dimorph of zoisite), epidote, hancockite, mukhinite, and piedmontite are members of this group.... (1999) Complete Story
