igneous

Basalt with Calcite Veins

Aphanitic mafic volcanic rock with CaCO3 inclusions

Hardness: 5-6 (basalt) / 3 (calcite veins); Color: Dark grey to black with white veining; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained) matrix; Cleavage: None in basalt, perfect rhombohedral in calcite.

Hardness: 5-6 (basalt) / 3 (calcite veins)
Color: Dark grey to black with white veining
Luster: Dull to sub-vitreous

Identified April 7, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The white veins formed later as mineral-rich groundwater circulated through fractures in the rock, depositing carbonate minerals.

Uses & applications

Used primarily in construction as crushed stone, concrete aggregate, and railroad ballast. Small weathered pieces are common in decorative landscaping or as garden stones.

Geological facts

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

Field identification & locations

Identify in the field by its heavy weight, dark color, and fine texture. The white veins will react (fizz) if a small drop of diluted hydrochloric acid or strong vinegar is applied, confirming calcite.

Other igneous specimens

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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