igneous
Greenstone / Basalt
Metabasalt (often containing Chlorite, Epidote, and Actinolite)
Hardness: 5-7 (Mohs); Color: Dark green, grayish-green, to nearly black; Luster: Dull to waxy when wet; Structure: Massive or fine-grained; Specific Gravity: 2.8-3.3.
- Hardness
- 5-7 (Mohs)
- Color
- Dark green, grayish-green, to nearly black
- Luster
- Dull to waxy when wet
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Physical properties
Hardness: 5-7 (Mohs); Color: Dark green, grayish-green, to nearly black; Luster: Dull to waxy when wet; Structure: Massive or fine-grained; Specific Gravity: 2.8-3.3.
Formation & geological history
Formed through the low-grade metamorphism of mafic igneous rocks (like basalt) under high pressure and low temperature, typically in subduction zones or mountain-building regions.
Uses & applications
Used as crushed stone for road base, decorative landscaping rock, and occasionally in artisanal jewelry as 'river jade' or 'greenstone' cabochons.
Geological facts
The green color is primarily due to the presence of chlorite and epidote minerals. In some regions, like New Zealand or the Pacific Northwest, specific types of greenstone are culturally significant and highly prized.
Field identification & locations
Identify in the field by its distinct greenish hue and smoothness when water-worn. Common in riverbeds draining volcanic mountain ranges. It is harder than a steel knife and will not fizz with acid.
