igneous

Amygdaloidal Basalt

Hardness: 5-6 (matrix); Color: Dark brown to reddish-brown (oxidized) with white/cream inclusions; Luster: Dull/earthy matrix with vitreous inclusions; Structure: Vesicular/Amygdaloidal; Specific Gravity: 2.8-3.0

Hardness: 5-6 (matrix)
Luster: Dull/earthy matrix with vitreous inclusions

Identified May 17, 2026More igneous →

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Physical properties

Formation & geological history

Formed from cooled volcanic lava where gas bubbles (vesicles) were later filled with secondary minerals like quartz, calcite, or zeolites through groundwater infiltration long after the initial eruption.

Uses & applications

Used primarily for geological study, landscaping, and as a decorative rock for collectors. In larger quantities, basalt is used for crushed stone in construction.

Geological facts

The word 'amygdule' comes from the Greek word for 'almond', referring to the almond-like shape of the mineral fillings in the rock. This specimen shows significant oxidation, giving it a rusty brown color.

Field identification & locations

Identify in the field by looking for a dark, heavy volcanic matrix containing distinct 'plugs' of lighter colored minerals. Commonly found in volcanic regions like the Lake Superior basin or Iceland.

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