igneous

Black Obsidian

Obsidian (Volcanic Glass, ~70% SiO2)

Hardness: 5-5.5; Color: Jet black to dark gray; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.

Hardness: 5-5
Color: Jet black to dark gray
Luster: Vitreous/Glassy

Identified May 24, 2026More igneous →

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Physical properties

Hardness: 5-5.5; Color: Jet black to dark gray; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6.

Formation & geological history

Formed from extrusive igneous activity where high-silica lava cools extremely rapidly, preventing crystal growth. Usually associated with geological ages from the Cenozoic to recent due to its tendency to devitrify over time.

Uses & applications

Used for making extremely sharp surgical scalpels, decorative jewelry (beads, cabochons), and ornamental carvings. Historically used for arrowheads and scrapers.

Geological facts

Because it has no crystal structure, its edges can reach almost molecular thinness, making it sharper than high-quality steel scalpels. It is technically a mineraloid rather than a mineral.

Field identification & locations

Identify by its glass-like appearance, smooth curved (conchoidal) fracture lines, and sharp edges. Common in volcanic regions such as Iceland, Mexico, and the western United States (e.g., Oregon, California).

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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