igneous

Basalt (Purple-tinted scoria/vesicular variety)

Extrusive mafic igneous rock (SiO2 range 45–52%)

Hardness: 5-6 (Mohs); Color: Dark grey to dull purple; Luster: Dull/Earthy; Structure: Vesicular (contains gas bubbles) and aphanitic (fine-grained); Specific Gravity: 2.8–3.0.

Hardness: 5-6 (Mohs)
Color: Dark grey to dull purple
Luster: Dull/Earthy

Identified March 20, 2026More igneous →

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Physical properties

Hardness: 5-6 (Mohs); Color: Dark grey to dull purple; Luster: Dull/Earthy; Structure: Vesicular (contains gas bubbles) and aphanitic (fine-grained); Specific Gravity: 2.8–3.0.

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The vesicular texture indicates gas was trapped in the lava during cooling. Geological age varies by locality, from recent Holocene flows to Precambrian periods.

Uses & applications

Commonly used as decorative landscaping stone (lava rock), in construction as aggregate for concrete or asphalt, and for railroad ballast.

Geological facts

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

Field identification & locations

Identify in the field by its weight (heavier than most volcanic rocks), fine-grained texture, and the presence of vesicles (holes). Common in volcanic regions like Hawaii, the Pacific Northwest (Columbia River Basalt Group), and Iceland.

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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)

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Magnetite

Magnetite (Fe3O4)

mineral