igneous

Obsidian

Obsidian (Volcanic Glass)

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

Hardness: 5-5

Identified May 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of silica-rich (felsic) lava, which prevents the growth of crystals. Typical in volcanic regions where lava is quenched by air or water.

Uses & applications

Historically used for making sharp tools like arrowheads and knives. Today it is used in ornamental jewelry, as a healing crystal, and in surgical scalpel blades because it can be sharper than steel.

Geological facts

Obsidian is often referred to as nature's glass. While it appears black, if sliced thin enough, it is often translucent. Some varieties like 'Snowflake' or 'Mahogany' obsidian have mineral inclusions that change their appearance.

Field identification & locations

Identify in the field by its distinctive conchoidal (shell-like) fracture patterns and sharp, glassy edges. It is commonly found in the western United States, Mexico, and Iceland near volcanic vents.

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