igneous

Obsidian

Obsidian (Volcanic Glass)

Mohs hardness: 5.0–6.0. Color: Black to dark grey. Luster: Vitreous/glassy. Crystal structure: Amorphous (non-crystalline). Cleavage: None, exhibits prominent conchoidal (shell-like) fracture. Specific gravity: 2.35–2.6.

Hardness: 5
Color: Black to dark grey
Luster: Vitreous/glassy

Identified March 31, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the rapid cooling of silica-rich felsic lava, which prevents crystal growth. It is typically found in geologically recent volcanic areas (Cenozoic era) because it is metastable and eventually devitrifies into fine-grained crystals.

Uses & applications

Historically used for making sharp tools like arrowheads and knives. Modern uses include surgical scalpel blades, ornamental jewelry, and gemstone carving.

Geological facts

Obsidian is technically a 'mineraloid' rather than a mineral because it lacks a crystal structure. It breaks with extremely sharp edges—thinner and sharper than a steel scalpel—which allows for cleaner incisions and faster healing in specialized surgeries.

Field identification & locations

Identify in the field by its distinct glassy appearance and characteristic conchoidal fracture patterns. Commonly found in volcanic regions like the American West, Mexico, Iceland, and Italy. Look for smooth, curved surfaces where the rock has chipped.

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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