igneous

Obsidian

Volcanic Glass (Amorphous Silica)

Hardness: 5-5.5 (Mohs scale); Color: Black, dark brown; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35-2.6

Hardness: 5-5
Color: Black, dark brown
Luster: Vitreous (glassy)

Identified May 21, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs scale); Color: Black, dark brown; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35-2.6

Formation & geological history

Formed from extrusive igneous activity when felsic lava (rich in silica) cools so rapidly that individual crystals do not have time to grow. It is common in volcanically active regions as young as the Quaternary period.

Uses & applications

Historically used for making extremely sharp arrowheads, knives, and surgical scalpels. In modern times, it is used for jewelry, decorative carvings, and as a semi-precious collector's stone.

Geological facts

Obsidian fractures with sharpness down to nearly molecular levels; it is actually sharper than the highest quality steel scalpels. Unlike most rocks, it is not a mineral because it lacks a regular crystal structure.

Field identification & locations

Identify by its characteristic glassy appearance and smooth, curved (conchoidal) fracture edges. Found in areas of past or present volcanic activity like the American West (Glass Buttes), Iceland, and Japan.

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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