igneous

Obsidian

Volcanic Glass (SiO2)

Hardness: 5-5

Identified February 12, 2026More igneous →

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Physical properties

Formation & geological history

Extrusive igneous rock formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in geologically young volcanic areas due to its instability over geological time.

Uses & applications

Used for making exceptionally sharp surgical blades, ornamental jewelry (cabochons), gaming dice, and decorative carvings. Historically used for arrowheads and knives.

Geological facts

Obsidian is so sharp that its edge is sometimes thinner than a human cell. It is 'mineral-like' but not a true mineral because it lacks a crystalline structure.

Field identification & locations

Identified by its smooth, curved conchoidal fractures and sharp edges. Commonly found in volcanic regions like the Cascades (USA), Iceland, and Mexico. Collectors should look for 'flow' patterns or 'sheen' varieties.

Other igneous specimens

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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