igneous

Obsidian

Volcanic glass (SiO2-rich extrusive igneous rock)

Hardness: 5–5.5 Mohs scale. Color: Deep black, sometimes translucent at edges. Luster: Vitreous (glassy). Structure: Amorphous (non-crystalline). Cleavage: None (exhibits conchoidal fracture). Specific Gravity: 2.35–2.6.

Hardness: 5–5
Color: Deep black, sometimes translucent at edges
Luster: Vitreous (glassy)

Identified March 29, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of silica-rich (felsic) lava, which prevents the growth of mineral crystals. It is geologically young as glass eventually devitrifies into minerals; mostly found in Cenozoic sites.

Uses & applications

Used historically for sharp tools and weapons (arrowheads, knives). Currently used in jewelry, scalpel blades for delicate surgeries due to its extreme sharpness, and as decorative stone.

Geological facts

Because it lacks a crystal structure, obsidian edges can reach near-molecular thinness, making it sharper than high-quality steel scalpels. It was widely traded as a valuable commodity in ancient civilizations.

Field identification & locations

Identify by its characteristic conchoidal (curved, shell-like) fracture and sharp edges. Common in volcanic regions such as the American West (Oregon, California), Mexico, Iceland, and Italy. Note: Look for the glassy texture and absence of visible grains.

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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

Blue Apatite

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

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral