metamorphic
Serpentinite
Serpentinite (complex of lizardite, chrysotile, and antigorite: (Mg,Fe)3Si2O5(OH)4)
Hardness: 2.5 to 5 on Mohs scale; Color: typically mottled shades of green, black, or yellow; Luster: waxy, greasy, or silky; Crystal Structure: Monoclinic; Cleavage: poor/irregular; Specific Gravity: 2.5–2.6.
- Hardness
- 2
- Color
- typically mottled shades of green, black, or yellow
- Luster
- waxy, greasy, or silky
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Physical properties
Hardness: 2.5 to 5 on Mohs scale; Color: typically mottled shades of green, black, or yellow; Luster: waxy, greasy, or silky; Crystal Structure: Monoclinic; Cleavage: poor/irregular; Specific Gravity: 2.5–2.6.
Formation & geological history
Formed through serpentinization, an exothermic metamorphic process where ultramafic rocks (like peridotite) from the Earth's mantle are hydrated by water at low temperatures near tectonic plate boundaries (subduction zones).
Uses & applications
Used historically as decorative building stone (Verde Antique), a source of magnesium, and occasionally for carvings or as a source of asbestos. High-quality varieties are used in jewelry as 'Green Marble'.
Geological facts
Serpentinite is the state rock of California. It is unique because it creates 'serpentine soils' that are toxic to most plants but host rare, endemic species adapted to high magnesium and heavy metal levels.
Field identification & locations
Identify by its characteristic green 'snake-skin' appearance, waxy feel, and softness (can often be scratched with a copper penny or knife). Commonly found in the Coast Ranges of California, the Appalachians, and the Alps.
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