igneous

Obsidian

Obsidian (Volcanic Glass, SiO2)

Hardness: 5-5.5 (Mohs scale); Color: Black, sometimes translucent on edges; Luster: Vitreous (glassy); Crystal structure: Amorphous; Cleavage: None (conchoidal fracture); Specific gravity: 2.35-2.6

Hardness: 5-5
Color: Black, sometimes translucent on edges
Luster: Vitreous (glassy)

Identified May 23, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs scale); Color: Black, sometimes translucent on edges; Luster: Vitreous (glassy); Crystal structure: Amorphous; Cleavage: None (conchoidal fracture); Specific gravity: 2.35-2.6

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, preventing crystal growth. Usually found in volcanic regions from the Cenozoic era or younger due to its tendency to devitrify over time.

Uses & applications

Used historically for sharp tools like arrowheads and knives. Modern uses include surgical scalpel blades, jewelry, decorative ornaments, and semi-precious gemstones.

Geological facts

Because it has no crystal structure, obsidian can be fractured to a thickness of only a few molecules, making it sharper than even high-quality steel scalpels. It is technically a mineraloid, not a mineral.

Field identification & locations

Identify in the field by its distinct conchoidal (shell-like) fracture pattern and extremely smooth, glassy surface. Common in volcanic active or historically volcanic areas like Oregon (USA), Mexico, 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