igneous

Obsidian

Obsidian (Volcanic Glass)

Hardness: 5-5.5 (Mohs), Color: Black to dark brown, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Cleavage: None/Conchoidal fracture, SG: 2.3-2.6

Hardness: 5-5

Identified May 14, 2026More igneous →

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Physical properties

Hardness: 5-5.5 (Mohs), Color: Black to dark brown, Luster: Vitreous/Glassy, Structure: Amorphous (non-crystalline), Cleavage: None/Conchoidal fracture, SG: 2.3-2.6

Formation & geological history

Formed from extrusive igneous activity when felsic lava cools rapidly with minimal crystal growth. Often found in volcanic regions from the Holocene or Pleistocene epochs.

Uses & applications

Used historically for sharp tools and weapons (scalpels, arrowheads). Modern uses include jewelry, decorative sculptures, and metaphysical collecting.

Geological facts

Because it is volcanic glass, it is metastable and eventually devitrifies into quartz over millions of years. It was a primary trade commodity in ancient empires like the Maya.

Field identification & locations

Identify by its glass-like appearance and smooth, curved (conchoidal) fractures that create razor-sharp edges. Look for it near rhyolitic volcanic sites like Glass Buttes or Yellowstone.

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