igneous

Black Obsidian

Volcanic Glass (SiO2 + impurities)

Hardness: 5–5.5 Mohs; Color: Jet black to dark gray; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (has conchoidal fracture); Specific Gravity: 2.4

Hardness: 5–5
Color: Jet black to dark gray
Luster: Vitreous/Glassy

Identified March 25, 2026More igneous →

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Physical properties

Hardness: 5–5.5 Mohs; Color: Jet black to dark gray; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (has conchoidal fracture); Specific Gravity: 2.4

Formation & geological history

Formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. It is relatively young geologically because it eventually devitrifies into quartz and feldspar crystals.

Uses & applications

Used in jewelry making (beads and pendants), high-end surgical scalpels (for cleaner incisions), and as a decorative stone in home decor.

Geological facts

Ancient civilizations used obsidian to create sharp arrowheads and mirrors. Because it lacks a crystal structure, its edges can be thinned down to nearly a single molecule in thickness.

Field identification & locations

Identify by its glass-like appearance, razor-sharp edges if broken, and smooth shell-like (conchoidal) fractures. Commonly found in volcanic regions like Iceland, Mexico, and the Western United States.

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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