igneous

Basalt with Quartz Veining

Basalt (Mafic Volcanic Rock with SiO2)

Hardness: 6-7 (Mohs scale), Color: Dark grey to black with white veins, Luster: Dull/Matte (matrix) to Vitreous (veins), Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8-3.0

Identified April 11, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava. The white veins are secondary hydrothermal deposits where silica-rich fluids filled fractures in the rock long after initial cooling.

Uses & applications

Commonly used as crushed stone for road base, concrete aggregate, and railroad ballast. Smooth river-worn specimens are often used in landscaping and aquarium decor.

Geological facts

Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. The white 'lightning' patterns are actually fractures that healed over millions of years.

Field identification & locations

Identify by its heavy weight, dark fine-grained matrix, and the presence of hard white veins that cannot be scratched by a steel nail. Commonly found in volcanic regions or as glacial till and river cobbles.

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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral