igneous

Black Obsidian with white veins

Volcanic Glass (70–75% SiO2)

Hardness: 5–6 Mohs; Color: Jet black with thin white streaks or inclusions; Luster: Vitreous (glass-like); Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.35–2.6.

Hardness: 5–6 Mohs
Color: Jet black with thin white streaks or inclusions
Luster: Vitreous (glass-like)

Identified March 15, 2026More igneous →

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Physical properties

Formation & geological history

Formed when high-silica lava cools too quickly for crystals to grow. The white veins are typically caused by trace amounts of internal stressors during cooling or inclusions of minerals like feldspar or quartz filling cracks.

Uses & applications

Commonly used for gemstone jewelry, decorative carvings, and scalpel blades (due to its ability to be fractured to a molecularly thin edge). Also popular in metaphysical collections.

Geological facts

Obsidian is technically a supercooled liquid, not a mineral, because it lacks a crystalline structure. Ancient civilizations throughout the Americas and Mediterranean used it for tools and projectile points.

Field identification & locations

Identify in the field by its characteristic smooth, curved (conchoidal) fractures and glass-like texture. Frequently found near geologically recent volcanic sites such as Oregon, Mexico, or Iceland. Collectors should look for its sharp edges.

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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

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Magnetite

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