metamorphic
Serpentinite
Serpentinite (complex silicate minerals including lizardite, chrysotile, and antigorite: (Mg,Fe)3Si2O5(OH)4)
Hardness: 3–6 on Mohs scale; Color: typically mottled shades of green, dark gray, or black; Luster: waxy to greasy; Crystal Structure: monoclinic/orthorhombic (varies by mineral); Cleavage: poor; Specific Gravity: 2.2 to 2.9.
- Hardness
- 3–6 on Mohs scale
- Color
- typically mottled shades of green, dark gray, or black
- Luster
- waxy to greasy
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Physical properties
Hardness: 3–6 on Mohs scale; Color: typically mottled shades of green, dark gray, or black; Luster: waxy to greasy; Crystal Structure: monoclinic/orthorhombic (varies by mineral); Cleavage: poor; Specific Gravity: 2.2 to 2.9.
Formation & geological history
Formed through serpentinization, an exothermic metamorphic process where mafic/ultramafic rocks (like peridotite) interact with water at low temperatures and high pressures, often at tectonic plate boundaries or near mid-ocean ridges.
Uses & applications
Used as an architectural stone for countertops and tiles, a source of magnesium, and for ornamental carvings. Polished and translucent varieties are sometimes sold as 'New Jade' or 'Bowenite'.
Geological facts
Serpentinite is the state rock of California. Some varieties contain chrysotile, which is a form of asbestos, though in solid rock form it is generally safe unless crushed or pulverized.
Field identification & locations
Identify in the field by its waxy 'snake-skin' appearance, slippery feel when wet, and mottled green-black color. Commonly found in ophiolite complexes, the Coast Ranges of California, the Alps, and the Himalayas.
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