metamorphic
Blue-green metamorphic cobble, probably serpentinite
Serpentinite (serpentine-group minerals; commonly lizardite, chrysotile, and antigorite), possibly altered mafic rock
AI-generated identification · may be incorrectDull to waxy luster; pale blue-green to gray-green, fine-grained and massive, with rounded weathered edges. Serpentine has Mohs hardness about 2.5–4, no obvious cleavage, and specific gravity roughly 2.5–2.6; the image does not show diagnostic crystals or veining.
Identified More metamorphic →
Explore Blue-green metamorphic cobble, probably serpentinite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dull to waxy luster; pale blue-green to gray-green, fine-grained and massive, with rounded weathered edges. Serpentine has Mohs hardness about 2.5–4, no obvious cleavage, and specific gravity roughly 2.5–2.6; the image does not show diagnostic crystals or veining.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate and alter during tectonic activity, commonly in ophiolites and fault zones. The cobble may have been transported and weathered from serpentinite-bearing Franciscan Complex rocks; exact age cannot be determined visually.
Uses & applications
Used as decorative stone, carvings, and occasionally aggregate, though asbestos-bearing varieties should not be cut, drilled, or crushed. Ordinary field specimens generally have little commercial value.
Geological facts
The reported location near 36.9°N, 121.4°W is geologically plausible for serpentinite and other Franciscan mélange rocks. Blue-green coloration can also result from chlorite, epidote, or copper staining.
Field identification & locations
Likely identification requires hardness, streak, and a fresh surface: serpentinite is typically softer than quartz and may show a greasy/waxy feel or slickensides. Common California alternatives include altered basalt, greenstone, or chlorite-rich rock; avoid dust because some serpentinite contains chrysotile asbestos.
More like this
