metamorphic
Serpentinite
Serpentinite (composed largely of serpentine group minerals including Antigorite, Lizardite, and Chrysotile, (Mg,Fe)3Si2O5(OH)4)
Hardness: 3-6 (Mohs scale), Color: Various shades of green, dark green to black-green, Luster: Waxy, greasy, or silky, Crystal Structure: Monoclinic/Orthorhombic (microcrystalline), Cleavage: Good but usually masses as a whole, SG: 2.2-2.9
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Physical properties
Hardness: 3-6 (Mohs scale), Color: Various shades of green, dark green to black-green, Luster: Waxy, greasy, or silky, Crystal Structure: Monoclinic/Orthorhombic (microcrystalline), Cleavage: Good but usually masses as a whole, SG: 2.2-2.9
Formation & geological history
Formed through 'serpentinization', a low-temperature metamorphic process where ultramafic rocks (like peridotite) from the Earth's mantle are hydrated by water at tectonic plate boundaries or mid-ocean ridges.
Uses & applications
Used as an ornamental stone in architecture, as a source for magnesium, historically for asbestos (chrysotile), and as a popular specimen for collectors and lapidary work.
Geological facts
Serpentinite is the official state rock of California. It often creates unique soil conditions (low in nutrients, high in heavy metals) that host rare endemic plant species.
Field identification & locations
Identified by its distinctive green color, 'snake-skin' waxy texture, and slippery feel. Commonly found in ophiolite belts where oceanic crust has been uplifted onto land, such as the Coast Ranges of California, the Alps, and parts of the Appalachians.
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