metamorphic
Greenstone with Epidote or Quartz veins
Metabasalt (Greenstone facies)
Hardness: 5-7 Mohs; Color: Dark green to grayish-black groundmass with light green or white veins; Luster: Dull to waxy; Structure: Microcrystalline with fractured veins; Specific Gravity: 2.8-3.3
- Hardness
- 5-7 Mohs
- Luster
- Dull to waxy
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Physical properties
Hardness: 5-7 Mohs; Color: Dark green to grayish-black groundmass with light green or white veins; Luster: Dull to waxy; Structure: Microcrystalline with fractured veins; Specific Gravity: 2.8-3.3
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks, such as basalt, under low temperature and pressure conditions (greenschist facies). This often occurs in oceanic crust subduction zones.
Uses & applications
Used in construction as crushed stone, in architectural facing, and sometimes as a lapidary material for decorative carvings or cabochons if the pattern is striking.
Geological facts
The green color is primarily due to the presence of minerals like chlorite, actinolite, and epidote. This specimen features hydrothermal vein filling where minerals precipitated in cracks during the metamorphic process.
Field identification & locations
Identify in the field by its characteristic dark green hue (often visible when wet), hardness, and the lack of visible foliation compared to schist. Found commonly in Ophiolite complexes and ancient mountain belts.
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