igneous

Basalt with Quartz/Feldspar Vein

Amygdaloidal Basalt with Plutonic intrusion (SiO2/KAlSi3O8)

Hardness: 6.0-7.0 (Mohs); Color: Dark grey to greenish-grey matrix with white/off-white translucent banding; Luster: Dull matrix with vitreous (glassy) veins; Crystal Structure: Phaneritic veins in an aphanitic groundmass; Cleavage: Subconchoidal fracture.

Hardness: 6
Luster: Dull matrix with vitreous (glassy) veins

Identified March 24, 2026More igneous →

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Physical properties

Formation & geological history

Formed through volcanic activity where basaltic lava cooled rapidly on the surface or in the shallow subsurface. The white banding occurred later through hydrothermal activity, where mineral-rich water filled cracks in the cooling rock and crystallized over millions of years.

Uses & applications

Primarily used as river rock, landscaping material, or road aggregate. While the basalt is used in construction, specimens like this are mostly of interest to amateur collectors as 'garden stones' or decorative pebbles.

Geological facts

The 'stripes' in such rocks are often called hydrothermal veins. They act as a geological record, showing where the rock once fractured under tectonic stress, allowing younger mineral fluids to inject into older volcanic material.

Field identification & locations

Identify in the field by its dark, heavy basaltic matrix contrasted against the hard, light-colored mineral veins that won't scratch with a steel nail. Commonly found in glacial till, riverbeds, and volcanic regions like the Pacific Northwest or the Great Lakes.

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral