igneous

Obsidian (specifically Silver Sheen Obsidian)

Volcanic Glass (approx. 70–75% SiO2 plus MgO, Fe3O4)

Hardness: 5–5.5 (Mohs scale); Color: Black with metallic silvery luster visible under light (sheen effect); Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.4

Hardness: 5–5
Luster: Vitreous/Glassy

Identified March 23, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed from the rapid cooling of silica-rich felsic lava (rhyolitic), which prevents crystal growth. The silver sheen is caused by tiny bubbles of gas or minuscule mineral inclusions trapped during flow. Most commercial obsidian is relatively young geologically (Cenozoic) because glass eventually devitrifies.

Uses & applications

Predominantly used for jewelry (beads, cabochons), ornamental carvings, and metaphysical collecting. Historically used for extremely sharp cutting tools and surgical blades.

Geological facts

Because it is a glass rather than a true mineral, it has no internal crystalline structure. Ancient civilizations like the Aztecs used obsidian for mirrors and sacrificial daggers. The silver sheen seen in these beads is a 'chatoyancy' effect caused by light reflecting off internal gas bubbles.

Field identification & locations

Identify by its glassy texture, conchoidal (shell-like) fracture patterns if chipped, and the characteristic 'glow' or sheen when rotated under a direct light source. Commonly found in volcanic regions such as Mexico, Iceland, and the Western United States.

Other igneous specimens

See all

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

Magnetite

Iron(II,III) oxide (Fe3O4)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral