metamorphic
Greenstone / Graywacke
Metagraywacke or Chlorite Schist
Hardness: 5-7 Mohs; Color: Dull green, olive, or grayish-green; Luster: Dull to waxy; Texture: Fine-grained, slightly foliated or massive; Composition: Quartz, feldspar, chlorite, and epidote.
- Hardness
- 5-7 Mohs
- Color
- Dull green, olive, or grayish-green
- Luster
- Dull to waxy
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Physical properties
Hardness: 5-7 Mohs; Color: Dull green, olive, or grayish-green; Luster: Dull to waxy; Texture: Fine-grained, slightly foliated or massive; Composition: Quartz, feldspar, chlorite, and epidote.
Formation & geological history
Formation occurs through the low-grade metamorphism of mafic igneous rocks or clay-rich sedimentary rocks like graywacke. Often associated with ancient subduction zones and mountain-building events (orogenies).
Uses & applications
Used historically for stone tools (celts/axes), modernly as decorative garden stones, road ballast, or as a source for crushed architectural stone.
Geological facts
Greenstone belts are some of the oldest known rock formations on Earth, dating back to the Archean Eon (over 2.5 billion years ago), containing vital information about early crustal development.
Field identification & locations
Identify by its characteristic 'sea-foam' or olive green hue caused by chlorite minerals. Look for it in riverbeds or coastal areas near metamorphic belts. It is tougher and denser than standard sandstone.
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