metamorphic
Veined metamorphic cobble, likely serpentinite
Serpentinite, commonly dominated by antigorite/lizardite with magnetite and cross-cutting quartz or calcite veins
AI-generated identification · may be incorrectTypically dark green-gray, waxy to subvitreous, massive, and fine-grained; Mohs hardness about 2.5–4, with irregular fracture and no obvious cleavage. The pale cream bands and end patch are likely quartz or calcite veins, while the black areas may contain magnetite or chromite.
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Physical properties
Typically dark green-gray, waxy to subvitreous, massive, and fine-grained; Mohs hardness about 2.5–4, with irregular fracture and no obvious cleavage. The pale cream bands and end patch are likely quartz or calcite veins, while the black areas may contain magnetite or chromite.
Formation & geological history
Formed when ultramafic mantle rock undergoes hydration and serpentinization, commonly along ancient oceanic crust and tectonic faults; exact age cannot be determined from the image. The contrasting veins formed later in fractures.
Uses & applications
Used as decorative and architectural stone, carving material, aggregate, and a collector specimen; attractive polished pieces may be sold as ornamental stone.
Geological facts
Serpentinite often feels relatively soft and may leave a faint greenish streak; some varieties contain asbestos-forming minerals, so avoid cutting, drilling, or generating dust.
Field identification & locations
Common in ophiolite belts and subduction-related mountain zones, including California, Italy, New Zealand, and the Appalachians. Confirm with a hardness test, streak, acid test on the pale vein, and ideally mineralogical analysis; visual identification is provisional.
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