igneous
Obsidian
Obsidian (Volcanic Glass, complex silicate)
Hardness: 5.0 to 6.0; Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
- Hardness
- 5
- Color
- Jet black
- Luster
- Vitreous/Glassy
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 5.0 to 6.0; Color: Jet black; Luster: Vitreous/Glassy; Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 2.4
Formation & geological history
Formed as an extrusive igneous rock when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Found in volcanic regions of any geological age, though rarely older than Cretaceous due to recrystallization.
Uses & applications
Used for making scalpel blades (sharper than steel), jewelry/gemstones, ornamental carvings, and historically for arrowheads and tools.
Geological facts
Obsidian breaks with a conchoidal fracture that produces edges thinner than a surgeon's scalpel. It is not technically a mineral because it lacks a crystalline structure.
Field identification & locations
Identify in the field by its glassy texture and curved, shell-like (conchoidal) fracture lines. Commonly found in Oregon, California, and Iceland. Exercise caution as edges are razor-sharp.
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
Sodalite
Sodalite - Na8(Al6Si6O24)Cl2
mineral
Blue Apatite
Apatite (Group), Ca5(PO4)3(F,Cl,OH)
mineral
Magnetite
Magnetite (Fe3O4)
mineral