igneous

Obsidian

Obsidian (Amorphous volcanic glass)

Hardness: 5–6 Mohs; Color: Black, sometimes dark brown or grey; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.3–2.6.

Hardness: 5–6 Mohs
Color: Black, sometimes dark brown or grey
Luster: Vitreous (glassy)

Identified April 7, 2026More igneous →

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Physical properties

Hardness: 5–6 Mohs; Color: Black, sometimes dark brown or grey; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.3–2.6.

Formation & geological history

Formed through the rapid cooling of felsic lava, which prevents the growth of crystals. Typically found in volcanic regions of various ages, from the Holocene to the Tertiary period.

Uses & applications

Historically used for weapons (arrowheads, blades). Currently used for surgical scalpels, decorative jewelry, gemstones, and as an ornamental stone in construction.

Geological facts

Obsidian is technically a supercooled liquid rather than a true mineral because it lacks a crystalline structure. It was highly traded in ancient civilizations as a precious commodity.

Field identification & locations

Identify in the field by its distinctive glassy appearance and sharp, curved (conchoidal) fracture edges. Commonly found in areas with recent rhyolitic volcanic activity like Iceland, Mexico, and the Western USA.

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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