mineral
Chiastolite
Andalusite variety Chiastolite (Al2SiO5)
Mohs hardness of 6.5 to 7.5; Color is typically gray, greenish, or brown with a distinct characteristic black cross pattern formed by carbonaceous inclusions; Luster is vitreous to dull; Crystal structure is orthorhombic; Specific gravity is 3.13 to 3.16.
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Physical properties
Mohs hardness of 6.5 to 7.5; Color is typically gray, greenish, or brown with a distinct characteristic black cross pattern formed by carbonaceous inclusions; Luster is vitreous to dull; Crystal structure is orthorhombic; Specific gravity is 3.13 to 3.16.
Formation & geological history
Formed through regional metamorphism of argillaceous (clay-rich) sediments under moderate temperatures and low-to-moderate pressures, where impurities of carbon become systematically trapped along the crystallographic axes during growth.
Uses & applications
Primarily used as a collector's mineral specimen, in lapidary arts, and sometimes fashioned into jewelry or talismans due to its natural cross marking.
Geological facts
Also known as the 'cross stone', chiastolite has historically been carried as an amulet or talisman for protection and good fortune because of the striking natural cross shape visible in cross-sections.
Field identification & locations
Easily identified by the dark, geometric cross pattern displayed on the surface or cross-section of the grayish-brown prismatic crystals. Commonly found in metamorphic terrains worldwide, including Spain, Russia, Australia, Chile, and the USA (California).
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