igneous

Obsidian

Obsidian (principally SiO2)

Hardness: 5-5.5 on Mohs scale; Color: Black, dark brown, or grey; Luster: Vitreous (glassy); Crystal structure: Amorphous (glassy); Cleavage: None (conchoidal fracture); Specific gravity: 2.3 - 2.6.

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

Identified March 29, 2026More igneous →

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Physical properties

Hardness: 5-5.5 on Mohs scale; Color: Black, dark brown, or grey; Luster: Vitreous (glassy); Crystal structure: Amorphous (glassy); Cleavage: None (conchoidal fracture); Specific gravity: 2.3 - 2.6.

Formation & geological history

Formed through the rapid cooling of silica-rich (rhyolitic) lava, which prevents crystal growth. It is relatively young geologically, usually less than a few million years old, as it eventually devitrifies into crystal rock over time.

Uses & applications

Historically used for edged tools like arrowheads and knives; currently used in luxury jewelry, experimental surgical scalpels, and decorative ornaments.

Geological facts

Because it has no mineral crystals and breaks with a conchoidal fracture, it can be honed to an edge only a few molecules thick, making it sharper than high-quality steel scalpels.

Field identification & locations

Identifiable by its smooth, glassy texture and sharp, shell-like (conchoidal) fracture lines. It is primarily found in volcanic regions such as the American Northwest, Iceland, Mexico, 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