igneous

Basalt (Vesicular)

Basalt (Mafic Extrusive Igneous Rock)

Hardness: 6-7 on Mohs scale; Color: dark grey to black but can weather to reddish-brown; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: dark grey to black but can weather to reddish-brown
Luster: Dull/Matte

Identified March 12, 2026More igneous →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: dark grey to black but can weather to reddish-brown; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8-3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. Most basalt specimens date from the Cenozoic to the Precambrian, found frequently at mid-ocean ridges and volcanic hotspots.

Uses & applications

Extensively used in construction as aggregate for roads, railroad ballast, and concrete; used in high-quality floor tiles and monuments; also processed into 'rock wool' for thermal insulation.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. It is also extremely common on the Moon and Mars, forming the dark 'seas' or maria seen on the lunar surface.

Field identification & locations

Identify in the field by its weight (dense), dark color, and fine-grained texture. To distinguish it from shale, look for a lack of layering and a higher density. Often found in volcanic fields, riverbeds draining volcanic areas, or coastal cliffs.

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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