igneous
Black Obsidian
Obsidian (Volcanic Glass)
Mohs hardness: 5-5.5. Color: Jet black to dark grey. Luster: Vitreous/glassy. Crystal structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.35-2.6.
- Hardness
- 5-5
- Color
- Jet black to dark grey
- Luster
- Vitreous/glassy
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Mohs hardness: 5-5.5. Color: Jet black to dark grey. Luster: Vitreous/glassy. Crystal structure: Amorphous (non-crystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.35-2.6.
Formation & geological history
Formed when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in areas of recent volcanic activity, dating from the Cenozoic era.
Uses & applications
Used for making surgical scalpels, arrowheads, ornamental jewelry, and crystal healing specimens.
Geological facts
Obsidian can be sharper than high-quality steel scalpels because it lacks a crystalline structure, allowing it to fracture down to nearly molecular thickness.
Field identification & locations
Identify by its smooth, glassy texture and distinctive shell-like (conchoidal) fractures. Found in volcanic regions like Iceland, Mexico, and the Western USA.
More like this
Other igneous specimens
Granite
Granite
Igneous
Granite
Granite
Igneous
Blue Apatite
Fluorapatite (Ca5(PO4)3F)
mineral
Dalmatian Jasper
Aplite with Arfvedsonite inclusions
igneous
Magnetite
Iron(II,III) oxide (Fe3O4)
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