igneous and sedimentary/mineral
Obsidian and Green Calcite
Volcanic Glass and Calcium Carbonate (CaCO3)
Obsidian: Hardness 5–5.5, black/dark grey, vitreous luster, amorphous structure, conchoidal fracture. Green Calcite: Hardness 3, pale green, vitreous to waxy luster, rhombohedral cleavage, specific gravity 2.7.
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Physical properties
Obsidian: Hardness 5–5.5, black/dark grey, vitreous luster, amorphous structure, conchoidal fracture. Green Calcite: Hardness 3, pale green, vitreous to waxy luster, rhombohedral cleavage, specific gravity 2.7.
Formation & geological history
Obsidian forms when felsic lava cools rapidly with minimal crystal growth. Calcite forms in sedimentary environments through chemical precipitation or from marine organism shells.
Uses & applications
Obsidian is used for surgical blades, jewelry (cabochons), and ancient weaponry. Green Calcite is used for decorative carvings, metaphysical collecting, and as a source of lime in industry.
Geological facts
Obsidian fractures with edges thinner than a surgeon's steel scalpel. Calcite is known for its double refraction and for fizzing instantly when exposed to weak acids like vinegar.
Field identification & locations
Identify Obsidian by its glassy sheen and sharp, curved edges. Identify Calcite by its softness (can be scratched by a penny) and rhombohedral shape. Common in volcanic regions and limestone deposits respectively.
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