metamorphic
Serpentinite (serpentinized ultramafic rock)
Serpentinite; chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), with magnetite, brucite, and residual olivine/pyroxene
AI-generated identification · may be incorrectTypically dark green to gray-green, mottled, waxy to dull luster, and fine-grained; hardness about 2.5–4 Mohs, massive with poor cleavage, and specific gravity roughly 2.5–2.7. The specimen’s rough green-black texture and pale veining are consistent with serpentinite, though a photo cannot confirm it.
Identified More metamorphic →
Explore Serpentinite (serpentinized ultramafic rock) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically dark green to gray-green, mottled, waxy to dull luster, and fine-grained; hardness about 2.5–4 Mohs, massive with poor cleavage, and specific gravity roughly 2.5–2.7. The specimen’s rough green-black texture and pale veining are consistent with serpentinite, though a photo cannot confirm it.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and altered by seawater or metamorphic fluids, commonly in ophiolites and subduction zones. Formation ages vary widely, from Precambrian to modern tectonic alteration.
Uses & applications
Used as decorative stone, carvings, countertops, and historically as “black marble”; some varieties are collected as mineral specimens. Avoid dust inhalation during cutting because certain serpentinite may contain asbestos-forming minerals.
Geological facts
Often displays slickensides, fibrous veins, and magnetite that can make it weakly magnetic. It is California’s state rock and commonly marks ancient oceanic crust exposed on land.
Field identification & locations
Look for greasy/waxy green surfaces, black magnetite specks, pale veins, low hardness, and a relatively heavy feel; common localities include California, Italy, New Zealand, Canada, and the Appalachian ophiolites.
More like this
