Chiastolite (Andalusite)

Hardness: 6.5-7.5 (Mohs scale), Color: Brownish grey with black cross, Luster: Vitreous to dull, Crystal structure: Orthorhombic, Cleavage: Good, Specific Gravity: 3.12-3.16

Formed through the regional metamorphism of clay-rich sediments (shale or phyllite). The cross pattern is created as carbonaceous inclusions are pushed to the edges of the growing crystal, forming a geometric pattern. Common in ancient metamorphic belts dating back millions of years.

Primary use is in jewelry (cabochons and pendants) and as a collector's mineral. Industrially, its parent mineral andalusite is used to manufacture high-temperature refractory materials for furnaces.

Also known as 'The Cross Stone' or 'Lapis Crucifer.' It has been used as a protective amulet for centuries; the cross pattern is entirely natural and not carved. It is a polymorphism of kyanite and sillimanite.

Identify by looking for the distinctive dark cross-shaped pattern in the center of an elongated prismatic or square crystal. Commonly found in locations like Spain (Santiago de Compostela), Australia, Brazil, and the United States (California/Massachusetts).