metamorphic
Serpentinite
Serpentinite (composed primarily of Serpentine group minerals like Antigorite, Lizardite, and Chrysotile)
Hardness: 3-6 on Mohs scale; Color: Dark green to black with pale green or white veining; Luster: Waxy, greasy, or silky; Crystal Structure: Monoclinic or Orthorhombic (often fibrous or massive); Cleavage: Good to perfect (in some varieties); Specific Gravity: 2.2-2.9.
- Hardness
- 3-6 on Mohs scale
- Color
- Dark green to black with pale green or white veining
- Luster
- Waxy, greasy, or silky
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Physical properties
Hardness: 3-6 on Mohs scale; Color: Dark green to black with pale green or white veining; Luster: Waxy, greasy, or silky; Crystal Structure: Monoclinic or Orthorhombic (often fibrous or massive); Cleavage: Good to perfect (in some varieties); Specific Gravity: 2.2-2.9.
Formation & geological history
Formed through the hydration of ultramafic rocks (like peridotite) from the Earth's mantle at low temperatures and high pressures, a process known as serpentinization. Common in tectonic plate boundaries and subduction zones.
Uses & applications
Used as decorative architectural stone, in sculptures (shale/soapstone varieties), as a source of asbestos in the past, and as a popular specimen for collectors due to its unique patterns.
Geological facts
Serpentinite is the official state rock of California. It often contains inclusions of magnetite, which can make specific specimens slightly magnetic.
Field identification & locations
Look for a slick, 'serpent-like' skin appearance with a waxy feel. It is commonly found in ophiolites and mountain ranges like the Appalachians, Alps, or the Coast Ranges of California. Collectors should look for high-contrast veining.
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