igneous
Obsidian with Matrix
Volcanic Glass (SiO2)
Hardness: 5-6 (Mohs); Color: Black with grayish-white matrix; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None (Conchoidal fracture); SG: 2.4
- Hardness
- 5-6 (Mohs)
- Color
- Black with grayish-white matrix
- Luster
- Vitreous/Glassy
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5-6 (Mohs); Color: Black with grayish-white matrix; Luster: Vitreous/Glassy; Structure: Amorphous; Cleavage: None (Conchoidal fracture); SG: 2.4
Formation & geological history
Formed from the rapid cooling of silica-rich lava which inhibits crystal growth. Can be found in volcanic regions of various ages, typically relatively young (Cenozoic) because glass eventually devitrifies.
Uses & applications
Historically used for sharp tools/weapons; currently used for scalpel blades, jewelry, and ornamental carvings.
Geological facts
Obsidian fractures into edges that can be much sharper than high-quality steel scalpels. It is technically a literal glass rather than a true mineral because of its amorphous nature.
Field identification & locations
Identified by its smooth, glassy texture and distinctive shell-like (conchoidal) fracture pattern. Commonly found in volcanic areas like the Western US, Mexico, and Iceland.
More like this
Other igneous specimens
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
Blue Apatite
Apatite (Group), Ca5(PO4)3(F,Cl,OH)
mineral
Sodalite
Sodalite - Na8(Al6Si6O24)Cl2
mineral
Magnetite
Magnetite (Fe3O4)
mineral