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Chalcedony:
Tectosilicates (A variety of quartz often with some iron and aluminum) SiO2 AKA: Agate, Bloodstone, Carnelian, Chrysoprase, Flint, Gem Silica, Heliotrope, Jasper, Moss agate, Onyx, Petrified Wood, Sard, Sardonyx |
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System: None; chalcedony is a microcrystalline variety of quartz. Appearance: White to gray, brown, blue, black and in several varieties as follows: carnelian and sard, clear to brownish red; sardonyx and onyx, sard and carnelian in layers; heliotrope and bloodstone, bright green with spots of red; agate, variegated, banded; moss agate, with mosslike or treelike inclusions; chrysoprase, apple-green; jasper, variegated and mottled red, yellow, brown; flint, whitish, dull gray, smokey brown to black. Physical Properties: Hardness: (7); Specific gravity: (2.6 - 2.64). Cleavage: None. Smooth conchoidal fracture; transparent when colorless, otherwise translucent to opaque as colors get darker. Dull waxy to vitreous luster depending on granularity and the variety; brittle to tough; sometimes weakly fluorescent. Chalcedony is amorphous without the vectorial properties of quartz. Similar species: Very few minerals are confused with chalcedony. Occurrence: Chalcedony is formed in several environments, generally near the surface of the earth where temperatures and pressures are relatively low. It commonly forms in the zone of alteration of lode and massive hydrothermal replacement deposits and as bodies of chert in chemical sedimentary rocks. Banded agates and colorful chalcedony occur as amygdules in basalt on the north shores of the Great Lakes in Ontario. Beautiful trees have been replaced by chalcedony at the Petrified Forest National Monument, Arizona. Agates of many colors are obtainable in a wide area in Chihuahua, Mexico. Miscellaneous: The name derives from Chalcedon, an ancient Greek city of Asia Minor. Chalcedony and varieties are used as gem and ornamental stones. Bloodstone is a birthstone for March; agate for May; carnelian or sardonyx for August. Most chalcedonies develop as a microcrystalline precipitate from aqueous solutions or as dehydration products of opal, in low-temperature environments. Conventional Wisdom: It was used as a sacred stone by Native American Indians, promoting stability within the ceremonial activities of the tribes. It has been used to provide a pathway for receiving thought transmissions. Chalcedony is useful for balancing the energy of the body, mind, emotions and spirit. It can used to improve the assimilation of minerals and to help combat build-up of materials in the veins. It is said to cure varying forms of dementia, to rectify senility and to improve mental stability. Belongs to the Astrological Signs of Cancer and Sagittarius. |