metamorphic
Greenstone / Serpentinite
Antigorite/Lizardite series (Mg,Fe)3Si2O5(OH)4
Hardness: 3-6 (Mohs); Color: Green, dark green, to grayish-green; Luster: Waxy to greasy; Crystal Structure: Monoclinic; Cleavage: Often basal, though usually massive; Specific Gravity: 2.5-3.2
- Hardness
- 3-6 (Mohs)
- Color
- Green, dark green, to grayish-green
- Luster
- Waxy to greasy
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Physical properties
Hardness: 3-6 (Mohs); Color: Green, dark green, to grayish-green; Luster: Waxy to greasy; Crystal Structure: Monoclinic; Cleavage: Often basal, though usually massive; Specific Gravity: 2.5-3.2
Formation & geological history
Formed via serpentinization, the low-temperature metamorphic hydration of ultramafic rock from the Earth's mantle, typically at tectonic plate boundaries or seafloor spreading centers.
Uses & applications
Used for carvings, ornamental stone, decorative architectural elements, and occasionally as a source of magnesium or asbestos (in fibrous varieties).
Geological facts
Greenstone is a broad field term for altered mafic/ultramafic rocks. It is associated with the 'Greenstone Belts' which contain some of the oldest known rocks on Earth and are often rich in gold and iron deposits.
Field identification & locations
Identify by its characteristic 'soapy' or greasy feel and greenish hue. Commonly found in coastal ranges or mountain belts with ophiolite complexes. It is often smoother and softer than surrounding basalt or quartz.
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