igneous

Obsidian

Obsidian (volcanic glass; primarily SiO2)

Hardness: 5–5.5 Mohs; Color: Black, deep brown, or grey (translucent at thin edges); Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35–2.6.

Hardness: 5–5
Color: Black, deep brown, or grey (translucent at thin edges)
Luster: Vitreous (glassy)

Identified January 1, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, preventing the growth of mineral crystals. It is typically found in volcanic regions of any geological age, though most surface samples are younger than the Cenozoic due to hydration over time.

Uses & applications

Historically used for razor-sharp tools and weapons. Modern uses include surgical scalpel blades, ornamental jewelry (cabochons), and high-end decorative objects.

Geological facts

Obsidian fractures with extremely sharp edges, often thinner than a high-quality steel blade. It is technically a 'mineraloid' rather than a mineral because it lacks a crystalline structure.

Field identification & locations

Identify in the field by its distinct conchoidal (shell-like) fracture patterns and glass-like reflection. Common in volcanic areas like Iceland, Mexico, Italy, and the western United States (e.g., Yellowstone or Glass Buttes).

Other igneous specimens

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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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral