igneous

Obsidian

Obsidian (Volcanic Glass, SiO2 + impurities)

Hardness: 5-5.5 on Mohs scale; Color: typically jet black but can be dark green or brown; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.4

Hardness: 5-5
Color: typically jet black but can be dark green or brown
Luster: Vitreous/Glassy

Identified March 28, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of felsic (silicic) lava, which prevents the growth of mineral crystals. It is found in volcanic regions where cooling was extremely fast, such as at the edges of basaltic lava flows or when lava enters water.

Uses & applications

Used historically for cutting tools, mirrors, and arrowheads due to its sharp edges. Modern uses include surgical scalps (for precision), jewelry, lapidary arts, and ornamental decoration.

Geological facts

Obsidian breaks with a conchoidal fracture, creating edges that are thinner and sharper than high-quality steel scalpels. It is technically a 'mineraloid' rather than a mineral because it lacks a crystalline structure.

Field identification & locations

Identify by its glass-like appearance, smooth texture, and curved, shell-like (conchoidal) fractures. Found in volcanic areas throughout the Americas, Iceland, and Italy. Collectors look for unique varieties like Snowflake or Mahogany obsidian.

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