Igneous

Obsidian Arrowhead

Volcanic Glass (70% or more SiO2)

Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35–2.6

Hardness: 5-5
Color: Jet black to dark grey
Luster: Vitreous (glassy)

Identified March 22, 2026More igneous →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 5-5.5 (Mohs scale); Color: Jet black to dark grey; Luster: Vitreous (glassy); Structure: Amorphous (non-crystalline); Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.35–2.6

Formation & geological history

Formed from rapidly cooling felsic lava that solidifies without sufficient time for crystal growth. Found in geologically recent volcanic areas (mostly Pliocene to Holocene). Common in the Pacific Northwest, Mexico, and Iceland.

Uses & applications

Historically used for cutting tools, scrapers, and arrowheads. Currently used in jewelry, decorative items, and high-precision surgical scalpel blades.

Geological facts

Obsidian fractures with an edge much thinner and sharper than a steel scalpel, down to a single molecule of thickness. It was a primary trade commodity in the ancient world, often called 'Black Gold' by Mesoamerican civilizations.

Field identification & locations

Identify in the field by its distinct glassy appearance, lack of grain, and sharp, curved edges. This specific specimen has been worked (knapped) by humans into a corner-notched projectile point shape.

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