igneous

Obsidian

Obsidian (Volcanic Glass, SiO2 + impurity isotopes)

Hardness: 5-5.5 (Mohs scale), Color: Jet black to dark grey, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6

Hardness: 5-5

Identified April 11, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs scale), Color: Jet black to dark grey, Luster: Vitreous/Glassy, Crystal Structure: Amorphous (non-crystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.35-2.6

Formation & geological history

Formed from extrusive igneous activity when silica-rich felsic lava cools extremely rapidly, preventing crystal growth. Most specimens found today are younger than 65 million years due to the glass being metastable and devitrifying over time.

Uses & applications

Used in high-quality surgical scalpels, jewelry (rings, pendants, beads), ornamental items, and historically for ultra-sharp weapons like arrows and knives.

Geological facts

Obsidian breaks with a conchoidal fracture, creating edges that are thinner than a steel scalpel—at the molecular level. It was the basis of the 'glass sword' (macuahuitl) used by Aztec warriors.

Field identification & locations

Identify by its glass-like appearance and smooth, curved (conchoidal) breaks. Look for translucency on thin edges. Commonly found in volcanic regions like the American West (Iceland, Mexico, Japan).

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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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral