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Serpentine is not a single mineral but a group of common rock-forming hydrous magnesium iron phyllosilicate minerals. The most common members are antigorite, lizardite, and chrysotile. These minerals are typically green, yellowish-green, or brownish-green, often with a mottled or variegated appearance resembling snakeskin, hence the name 'serpentine' (from Latin 'serpens' meaning snake). Serpentine minerals are characteristic components of serpentinite, a metamorphic rock formed from the hydration of ultramafic rocks.
How to Identify
- Color
- Typically shades of green (light to dark, yellowish-green, olive-green, bluish-green), sometimes brownish, blackish, or mottled.
- Luster
- Greasy, waxy, silky (especially chrysotile), or dull.
- Texture
- Smooth, soapy, or fibrous. Often feels slippery to the touch.
- Crystal Form
- Massive, platy (antigorite), fine-grained (lizardite), or fibrous (chrysotile). Individual crystals are rarely macroscopic.
- Cleavage
- Perfect basal cleavage in antigorite and lizardite, but often not observed in massive forms. Chrysotile exhibits fibrous parting.
- Geological Environment
- Associated with ophiolite complexes, subduction zones, and areas where oceanic crust or mantle rocks have been uplifted and hydrated. Found in metamorphic terrains derived from ultramafic protoliths.
Key Facts
- Hardness: 2.5-5.0 on Mohs scale (varies by mineral: chrysotile ~2.5-3, lizardite ~2.5-4, antigorite ~3.5-5)
- Specific Gravity: 2.5-2.9 g/cm (varies slightly by mineral)
- Crystal System: Monoclinic (chrysotile, lizardite), Orthorhombic (antigorite)
- Color: Green, yellowish-green, brownish-green, blackish-green, often mottled
- Luster: Greasy, waxy, silky (fibrous varieties), dull
- Transparency: Translucent to opaque
- Fracture: Conchoidal to splintery (antigorite), fibrous (chrysotile)
- Cleavage: Perfect basal cleavage (001) in antigorite and lizardite, but often not visible in massive forms. Chrysotile exhibits fibrous parting.
- Composition: Hydrous magnesium iron phyllosilicate
Quick Check
- Color: Green to yellowish-green, often mottled
- Luster: Greasy, waxy, or silky
- Streak: White
Physical Characteristics
- Crystal Habit: Massive, platy, lamellar, fibrous, fine-grained, pseudomorphic after olivine or pyroxene.
- Cleavage Type: Perfect basal (001) in antigorite and lizardite, but often indistinct in massive aggregates. Chrysotile has fibrous parting.
- Fracture Type: Conchoidal to splintery (antigorite), fibrous (chrysotile).
- Tenacity: Brittle to tough (antigorite), flexible (chrysotile fibers).
- Luster Type: Greasy, waxy, silky, dull.
Formation
Serpentine group minerals form through the serpentinization of ultramafic rocks (peridotite, dunite) in the presence of water, typically at low to moderate temperatures (200-500 C) and pressures. This process involves the hydration and metamorphic alteration of olivine and pyroxene minerals.
Usage
Ornamental stone, carving material, architectural facing, source of asbestos (chrysotile), industrial filler, talc substitute. Historically used for decorative objects and jewelry.
Age Distribution
Found in rocks of various ages, from Precambrian to Cenozoic, wherever ultramafic rocks have undergone hydrothermal alteration.
Where to Find
California, USA
Extensive serpentinite belts, particularly in the Coast Ranges and Sierra Nevada foothills, often associated with ophiolites.
Appalachian Mountains, USA/Canada
Occurrences in various states and provinces, reflecting ancient oceanic crust and mantle obduction.
Italy
Notable for decorative varieties, particularly in the Alps and Apennines.
New Zealand
Source of Bowenite, a translucent, hard variety of antigorite, often used for carving.
Russia (Urals)
Significant deposits of chrysotile asbestos and decorative serpentinite.
Cyprus
Part of the Troodos Ophiolite, a classic example of oceanic crust.
Finding Tips
Geological Context
Look for serpentine in areas mapped as ultramafic rocks (peridotite, dunite) or ophiolite complexes. These are often found in mountain belts or ancient suture zones.
Associated Minerals
Serpentine often occurs with chromite, magnetite, talc, magnesite, and sometimes relict olivine or pyroxene.
Field Appearance
Serpentinite outcrops often have a distinctive greenish-black, smooth, and sometimes slickensided appearance due to tectonic deformation. The soil above serpentinite can be reddish-brown due to iron oxidation.
Safety Precaution: Asbestos
Be extremely cautious when collecting fibrous varieties of serpentine, particularly chrysotile. Chrysotile is a form of asbestos, and inhalation of its fibers can cause serious lung diseases, including asbestosis, lung cancer, and mesothelioma. Avoid disturbing or breaking fibrous serpentine. Do not saw, grind, or sand it without proper respiratory protection (P100 respirator) and ventilation. If unsure, treat fibrous material as potentially hazardous and avoid direct contact or inhalation of dust.
Similar Rocks
Nephrite Jade
Nephrite (a variety of actinolite/tremolite)
Also known as: Jade
Chlorite
Chlorite Group Minerals
Also known as: Chlorite Group
Talc
Talc
Also known as: Steatite
Scientific Classification
- Mineral Class
- Phyllosilicates
- Group
- Serpentine Group
- Crystal System
- Monoclinic (chrysotile, lizardite), Orthorhombic (antigorite)
- Chemical Formula
- MgSiO(OH) (idealized for pure magnesium serpentine, but often contains Fe and Al)
- Composition
- Hydrous magnesium iron silicate. The general formula is (Mg,Fe)SiO(OH). The three main polymorphs are antigorite (platy), lizardite (platy/fine-grained), and chrysotile (fibrous).
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