sedimentary
Green Calcite (Onyx Marble)
Carbonate mineral (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale; Color: Pale green to lime green; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Fracture: Conchoidal.
- Hardness
- 3 on Mohs scale
- Color
- Pale green to lime green
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 3 on Mohs scale; Color: Pale green to lime green; Luster: Vitreous to waxy; Crystal Structure: Trigonal/Hexagonal; Cleavage: Perfect rhombohedral; Fracture: Conchoidal.
Formation & geological history
Formed in sedimentary environments, often through the precipitation of calcium-rich waters in caves (speleothems) or hydrothermal veins. Common in limestone deposits and hot spring areas.
Uses & applications
Used for lapidary work, decorative carving, ornamental sculptures, metaphysical healing practices, and as architectural stone (often mislabeled as 'Onyx' in the tile industry).
Geological facts
Green calcite is often mistakenly referred to as 'German Onyx' or 'Mexican Onyx' in the trade, but it is actually a calcium carbonate rather than a variety of chalcedony. It is highly sensitive to acid.
Field identification & locations
Identified in the field by its low hardness (can be scratched with a copper penny or knife), rhombohedral cleavage, and vigorous effervescence when exposed to dilute hydrochloric acid. Primarily found in Mexico and Brazil.
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