igneous

Obsidian

Volcanic Glass (SiO2 + impurities)

Hardness: 5-5.5 (Mohs scale); Color: Jet black (sometimes brown or green); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.4

Hardness: 5-5
Color: Jet black (sometimes brown or green)
Luster: Vitreous/Glassy

Identified April 4, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs scale); Color: Jet black (sometimes brown or green); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.4

Formation & geological history

Formed from rapid cooling of silica-rich (rhyolitic) lava, which prevents crystal growth. It is found in volcanic regions of various geological ages, often in marginal zones of lava flows.

Uses & applications

Used for making scalpels (due to extreme sharpness), fashion jewelry, decorative ornaments, and historically for tools and weapons such as arrowheads and mirrors.

Geological facts

Obsidian fractures with edges so thin they can be many times sharper than a steel scalpel. Native Americans used it for trade across vast networks for thousands of years.

Field identification & locations

Identify by its characteristic conchoidal (shell-like) fracture and sharp edges. It is common in areas with recent volcanic activity like Yellowstone, the Cascades, or the Andes mountains.

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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