metamorphic
Greenstone with Epidote or Quartz Vein
Epidiorite or Metabasalt (composed largely of Chlorite, Epidote, and Amphibole)
Hardness: 5-7 Mohs; Color: Dull grayish-green with light yellowish-green or white veins; Luster: Dull/Earthy to slightly Waxy; Structure: Fine-grained with cross-cutting veins; Specific Gravity: 2.8-3.0
- Hardness
- 5-7 Mohs
- Color
- Dull grayish-green with light yellowish-green or white veins
- Luster
- Dull/Earthy to slightly Waxy
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Physical properties
Hardness: 5-7 Mohs; Color: Dull grayish-green with light yellowish-green or white veins; Luster: Dull/Earthy to slightly Waxy; Structure: Fine-grained with cross-cutting veins; Specific Gravity: 2.8-3.0
Formation & geological history
Formed through low-grade regional metamorphism of mafic igneous rocks (like basalt) under high pressure and low temperatures. Often found in ancient volcanic island arc environments or mountain-building regions.
Uses & applications
Used primarily as decorative garden stone, crushed stone for road construction, and occasionally for minor ornamental carvings. High-quality varieties like 'Nephrite' are used in jewelry.
Geological facts
Greenstone is a broad term for altered basic igneous rocks. The 'green' color comes from the presence of minerals like chlorite, actinolite, and epidote. Similar rocks in the Lake Superior region are known as 'Isle Royale Greenstone'.
Field identification & locations
Identify by its distinctive pistachio or forest green color and hardness (it should be difficult to scratch with a steel knife). Commonly found in stream beds or glacial till in regions with ancient tectonic activity like the Appalachian and Ural mountains.
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