igneous

Obsidian

Volcanic Glass (Amorphous Silicon Dioxide)

Hardness: 5-5.5; Color: Deep black, sometimes translucent at edges; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35-2.60

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

Identified January 12, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, preventing crystal growth. It typically originates from extrusive volcanic eruptions during the Cenozoic era or younger, as glass eventually devitrifies into crystalline rock over millions of years.

Uses & applications

Used historically for razor-sharp tools and weapons like arrowheads. Today, it is used for high-end surgical scalpels, decorative jewelry (cabochons), and ornamental carvings.

Geological facts

Obsidian fractures with edges so thin they can reach molecular levels, making it sharper than high-quality steel scalpels. In Aztec culture, it was crafted into 'Macuahuitl' clubs and used for ritual mirrors.

Field identification & locations

Identify by its smooth, glassy texture and razor-sharp curved (conchoidal) fracture lines. Commonly found in volcanic regions such as the American Northwest (Oregon), Iceland, Mexico, and the Lipari Islands. Collectors should look for 'flow' lines or 'snowflakes' (cristobalite inclusions) within the glass.

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

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Magnetite

Magnetite (Fe3O4)

mineral