igneous

Scoria (Lava Rock)

Vesicular Basalt / Scoria

Hardness: 5-6 Mohs; Color: Dark brown, black, or reddish-purplish; Luster: Dull to sub-vitreous; Structure: Highly vesicular (honeycombed with gas bubbles); Specific Gravity: Relatively low/lightweight due to air pockets.

Hardness: 5-6 Mohs
Color: Dark brown, black, or reddish-purplish
Luster: Dull to sub-vitreous

Identified March 21, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the rapid cooling of gas-rich mafic (basaltic) lava. As lava erupts from a volcano, dissolved gases come out of solution and form bubbles; if the rock cools before the bubbles pop, the holes are preserved. Typically associated with youthful volcanic activity (Cenozoic era).

Uses & applications

Used extensively in landscaping, gas grill lava rocks, high-temperature insulation, lightweight concrete aggregate, and road drainage systems.

Geological facts

Scoria differs from pumice in that it has larger vesicles and thicker cell walls, making it sink in water, whereas pumice often floats. It is a primary component of cinder cones, which are the most common type of volcano on Earth.

Field identification & locations

Identify by its 'Swiss cheese' appearance, dark color, and rough, abrasive texture. Commonly found in volcanic fields such as those in Iceland, Hawaii, Italy, and the Western United States (Arizona, New Mexico). Many collectors pick these up as 'souvenirs' of volcanic regions.

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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