igneous

Obsidian

Obsidian (Volcanic Glass)

Hardness: 5-5.5 Mohs; Color: Black, sometimes dark green or brown; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.

Hardness: 5-5
Color: Black, sometimes dark green or brown
Luster: Vitreous/Glassy

Identified May 23, 2026More igneous →

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Physical properties

Hardness: 5-5.5 Mohs; Color: Black, sometimes dark green or brown; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.

Formation & geological history

Formed by the rapid cooling of silica-rich (felsic) lava, which prevents the formation of mineral crystals. Usually found in geologically young volcanic areas (Pliocene to Holocene).

Uses & applications

Historically used for arrowheads and knives due to sharp edges. Today used in scalpel blades, jewelry, and as a semi-precious gemstone.

Geological facts

Obsidian is biologically inert and can be fashioned into blades far sharper than high-quality steel scalpels. It is technically a glass rather than a mineral because it lacks a crystalline structure.

Field identification & locations

Identify by its smooth, glassy texture and razor-sharp conchoidal (shell-like) fracture edges. Commonly found in volcanic regions of Oregon, California, and Iceland.

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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