metamorphic
Greenstone / Serpentinite Pebble
Serpentinite (Hydrated Magnesium Silicate, Mg3Si2O5(OH)4)
Hardness: 2.5–5.5 on Mohs scale; Color: Grayish-green to olive green with waxy or dull finish; Luster: Dull to waxy/greasy; Crystal structure: Microcrystalline/massive; Cleavage: Poor to none in rounded water-worn pebbles.
- Hardness
- 2
- Color
- Grayish-green to olive green with waxy or dull finish
- Luster
- Dull to waxy/greasy
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Physical properties
Hardness: 2.5–5.5 on Mohs scale; Color: Grayish-green to olive green with waxy or dull finish; Luster: Dull to waxy/greasy; Crystal structure: Microcrystalline/massive; Cleavage: Poor to none in rounded water-worn pebbles.
Formation & geological history
Formed through the metamorphic transformation of ultramafic igneous rocks (such as peridotite) in subduction zones or oceanic crust environments subjected to high pressures and hydrothermal action (serpentinization). Smoothness results from wave and stream action.
Uses & applications
Used primarily as decorative beach stones, tumbling material, local carving material, and ornamental stone. High-grade nephrite or jadeite variations are used in lapidary art and jewelry.
Geological facts
Serpentinite is the official state rock of California. These smooth green pebbles are frequently found along coastal beaches and riverbeds near subduction zone terranes, such as the Franciscan Complex along the U.S. Pacific Northwest coast.
Field identification & locations
Can be identified in the field by its smooth, water-rounded surface, muted grayish-green to sea-green color, soft-to-medium hardness, and characteristic waxy feel. Highly abundant along gravel beaches near metamorphic bedrock formations.
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