igneous

Obsidian

Volcanic Glass (mostly SiO2)

Hardness: 5-5.5; Color: Jet black, sometimes translucent brown on thin edges; Luster: Vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.35-2.6

Hardness: 5-5
Color: Jet black, sometimes translucent brown on thin edges
Luster: Vitreous (glassy)

Identified March 13, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of felsic lava, which prevents crystal growth. It is usually found in geologically young volcanic areas (Cenozoic era) because it eventually devitrifies into crystals.

Uses & applications

Used historically for sharp tools and weapons (arrowheads, knives); modern uses include surgical scalpels, ornamental jewelry, and decorative gemstones.

Geological facts

Because it breaks with a conchoidal fracture, it produces edges thinner and sharper than a steel scalpel. Native Americans traded obsidian over hundreds of miles throughout North America.

Field identification & locations

Identify in the field by its glassy texture and razor-sharp curved edges when broken. Commonly found in volcanic regions of Oregon, California, Iceland, and Mexico.

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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