igneous

Basalt with Quartz/Calcite Veins

Amygdaloidal Basalt (SiO2 or CaCO3 inclusions)

Hardness: 6-7 (basalt matrix); Color: dark grey to black with white/cream veins; Luster: dull/matt matrix with vitreous veins; Crystal structure: fine-grained (aphanitic) matrix.

Hardness: 6-7 (basalt matrix)
Color: dark grey to black with white/cream veins
Luster: dull/matt matrix with vitreous veins

Identified March 21, 2026More igneous →

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Physical properties

Hardness: 6-7 (basalt matrix); Color: dark grey to black with white/cream veins; Luster: dull/matt matrix with vitreous veins; Crystal structure: fine-grained (aphanitic) matrix.

Formation & geological history

Formed from the rapid cooling of basaltic lava at the Earth's surface. The white veins are secondary mineralizations (usually quartz or calcite) deposited by hydrothermal fluids filling fractures and cracks long after the initial cooling.

Uses & applications

Common basalt is used in construction as road base, concrete aggregate, and railroad ballast. Veined specimens are often collected as decorative river/beach stones or for lapidary work.

Geological facts

Basalt is the most common rock in the Earth's crust and makes up most of the ocean floor. The white 'stripes' are geological records of seismic activity or stress that cracked the rock, which was then 'healed' by mineral-rich water.

Field identification & locations

Identify in the field by its heavy weight (high density), dark color, and high hardness (will scratch glass if it's quartz-veined). Commonly found on volcanic coastlines and riverbeds. For collectors, look for high contrast between the dark matrix and bright white veins.

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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.

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

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Magnetite

Magnetite (Fe3O4)

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