Igneous

Obsidian

Volcanic Glass (Primary composition: SiO2 - Silicon Dioxide)

Hardness: 5-6 Mohs scale; Color: Jet black (can be dark green or brown); Luster: Vitreous/glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6

Hardness: 5-6 Mohs scale
Color: Jet black (can be dark green or brown)
Luster: Vitreous/glassy

Identified March 15, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of silica-rich felsic lava, which prevents the growth of mineral crystals. Typically found in volcanic areas with relatively recent eruptions (Cenozoic era).

Uses & applications

Used for surgical scalpel blades (sharper than steel), ornamental jewelry (cabochons), interior decor, and as a popular semi-precious stone for collectors and metaphysical uses.

Geological facts

Because it doesn't have a crystal structure, obsidian edges can reach molecular thinness. In pre-Columbian Mesoamerica, it was used to create the 'Macuahuitl' (a wooden sword with obsidian blades).

Field identification & locations

Identify in the field by its distinctive 'conchoidal' (shell-like) fracture patterns and sharp edges. Common in regions like the Western United States (Oregon, California), Mexico, and Iceland. Collectors should look for unique variants like 'Snowflake' or 'Rainbow' obsidian.

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral