metamorphic
Chiastolite
Andalusite (Al2SiO5) with carbonaceous inclusions
Hardness: 6.5 - 7.5; Color: Brown, grey, or yellowish-white with a black cross; Luster: Vitreous to dull; Crystal Structure: Orthorhombic; Cleavage: Good in two directions; Specific Gravity: 3.13 - 3.16.
- Hardness
- 6
- Color
- Brown, grey, or yellowish-white with a black cross
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5 - 7.5; Color: Brown, grey, or yellowish-white with a black cross; Luster: Vitreous to dull; Crystal Structure: Orthorhombic; Cleavage: Good in two directions; Specific Gravity: 3.13 - 3.16.
Formation & geological history
Forms during regional metamorphism of clay-rich sediments (pelitic rocks). The cross is formed when carbonaceous material or graphite is squeezed into the corners of growing crystals.
Uses & applications
Used primarily as a gemstone in necklaces or pendants, as a collector specimen, and historically as a protective amulet due to the cross pattern.
Geological facts
Also known as the 'Cross Stone', it has been used since ancient times as a symbol of faith and protection. It is a variety of the mineral andalusite.
Field identification & locations
Identify in the field by the distinct black cruciform pattern when sliced or polished. Common locations include Spain (Santiago de Compostela), Brazil, Chile, and the United States (California/Massachusetts).
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