metamorphic
Greenstone (Chert)
Microcrystalline Silica (SiO2) with chlorite/epidote inclusions
Hardness: 6.5-7 on Mohs scale; Color: Dull olive green with grey/black patches; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Dull olive green with grey/black patches
- Luster
- Waxy to dull
Identified More metamorphic →
Explore Greenstone (Chert) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Dull olive green with grey/black patches; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the low-grade metamorphism of basaltic rocks or silica-rich seafloor sediments. The green color typically arises from the presence of chlorite, actinolite, or epidote created during the hydrothermal alteration process.
Uses & applications
Historically used for stone tools (axes, arrowheads) due to its conchoidal fracture. Modernly used for landscaping, as a minor gemstone (tumbled), or as decorative gravel.
Geological facts
The term 'Greenstone' is a catch-all field term for any dark, greenish altered igneous rock. It is a major component of 'Greenstone Belts', which contain some of Earth's oldest known crustal rocks.
Field identification & locations
Identify by its waxy texture, hardness (it will scratch glass), and characteristic dull green hue. It is commonly found in ancient mountain belts and regions with volcanic history, like the Pacific Northwest or the Great Lakes region.
