metamorphic
Greenschist (containing Epidote and Quartz)
Greenschist (Epidote-Chlorite-Actinolite Schist)
Hardness: 6-7 (Epidote/Quartz components); Color: Foliated olive to dark green with translucent white/grey quartz veins; Luster: Vitreous to pearly; Crystal structure: Monoclinic (Epidote) and Hexagonal (Quartz); Cleavage: Perfect in one direction for schistose minerals.
- Hardness
- 6-7 (Epidote/Quartz components)
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-7 (Epidote/Quartz components); Color: Foliated olive to dark green with translucent white/grey quartz veins; Luster: Vitreous to pearly; Crystal structure: Monoclinic (Epidote) and Hexagonal (Quartz); Cleavage: Perfect in one direction for schistose minerals.
Formation & geological history
Formed via regional metamorphism of mafic igneous rocks (like basalt) under low-temperature, high-pressure conditions (Greenschist facies). This process often occurs at convergent plate boundaries and can date from the Precambrian to the Cenozoic.
Uses & applications
Used primarily as decorative stone, crushed aggregate for construction, and as a low-grade pigment or collector's specimen for studying metamorphic facies.
Geological facts
The green color of the rock is primarily due to minerals like chlorite, epidote, and actinolite. The presence of large, clear-to-milky quartz chunks alongside the green matrix indicates hydrothermal activity during the metamorphic process.
Field identification & locations
Identify in the field by its distinct green hue and 'schistose' foliated texture that allows it to split into flakes. It is commonly found in mountain belts like the Appalachians, Alps, or the Coast Ranges of California. Collectors should look for areas where quartz veins intersect the green host rock.
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