igneous

Black Obsidian

Volcanic Glass (SiO2 + impurities)

Hardness: 5-5.5 (Mohs scale), Color: Jet black to dark grey, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6

Hardness: 5-5

Identified March 4, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs scale), Color: Jet black to dark grey, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6

Formation & geological history

Formed as an extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in regions with geologically recent volcanic activity.

Uses & applications

Historically used for weapons (arrowheads, blades) and surgical scalpels. Currently used in jewelry, ornamental carvings, and gemstone therapy.

Geological facts

Because it is glass and lacks a crystalline structure, obsidian edges can reach molecular thinness, making them sharper than steel surgical scalpels.

Field identification & locations

Identify by its iconic conchoidal (shell-like) fracture and sharp edges. Found in volcanic fields such as those in Mexico, Iceland, and the Western United States. Collectors look for high clarity and lack of air bubbles.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous