igneous

Basalt with Quartz Veining

Amygdaloidal Basalt (predominately SiO2 and (Na,Ca)(Si,Al)4O8)

Hardness: 6-7 Mohs; Color: Dark grey to black with white/translucent veins; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained matrix); Cleavage: None (conchoidal fracture).

Hardness: 6-7 Mohs
Color: Dark grey to black with white/translucent veins
Luster: Dull to sub-vitreous

Identified April 12, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: Dark grey to black with white/translucent veins; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained matrix); Cleavage: None (conchoidal fracture).

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near a planetary surface. The white veins are later hydrothermal secondary mineral infillings (quartz or calcite) deposited in fractures.

Uses & applications

Commonly used in construction as crushed stone, road base, and concrete aggregate. Occasional use in ornamental landscaping.

Geological facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found in abundance on the Moon and Mars.

Field identification & locations

Identify by its heavy weight, dark color, and fine-grained texture. To distinguish from surface staining, look for the 'vein' cutting through the rock body. Commonly found in volcanic fields and coastal outcrops.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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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

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Magnetite

Magnetite (Fe3O4)

mineral