metamorphic
Greenstone pebble (likely serpentinite)
Serpentinite, composed chiefly of serpentine-group minerals (e.g., lizardite or antigorite); identification from the photo is tentative
AI-generated identification · may be incorrectOpaque, muted green-gray, smooth and rounded by abrasion, with a faint waxy sheen. Serpentine minerals are about 2.5–4 Mohs, generally fine-grained, and lack visible crystal faces; specific gravity is typically around 2.5–2.6.
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Physical properties
Opaque, muted green-gray, smooth and rounded by abrasion, with a faint waxy sheen. Serpentine minerals are about 2.5–4 Mohs, generally fine-grained, and lack visible crystal faces; specific gravity is typically around 2.5–2.6.
Formation & geological history
Forms when water alters magnesium-rich ultramafic rocks, commonly in oceanic crust and subduction zones; the pebble’s geological age and source cannot be determined from appearance alone.
Uses & applications
Attractive pieces are used for carving, ornament, and jewelry; massive serpentinite has also been used as decorative building stone.
Geological facts
The name greenstone is broad and can refer to several green rocks, so color alone cannot establish that this pebble is serpentinite.
Field identification & locations
Its smooth, water-worn shape suggests transport by a stream or shore. A reliable identification requires tests or close examination for texture, hardness, and mineral composition.
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