igneous

Amygdaloidal Basalt

Basalt with secondary mineral infilling (commonly Zeolite, Calcite, or Quartz)

Hardness: 5-6 (matrix); Color: Dark grey to black matrix with white or green spots (amygdules); Luster: Dull matrix with vitreous/pearly inclusions; Texture: Aphanitic with vesicles; Crystal Structure: Microcrystalline.

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

Identified May 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the rapid cooling of magnesium-rich and iron-rich lava. Gas bubbles (vesicles) trapped in the cooling lava are later filled with secondary minerals precipitated from hydrothermal fluids flowing through the rock.

Uses & applications

Used as decorative stones, in landscaping, as road aggregate, and as a popular specimen for educational kits or amateur mineral collecting.

Geological facts

The term 'amygdule' comes from the Greek word 'amygdala', meaning almond, referring to the typical shape of the mineral-filled gas bubbles. Many famous Lake Superior agates began as amygdules in basalt.

Field identification & locations

Identified by the dark, heavy volcanic matrix containing distinct, rounded lighter-colored mineral 'spots'. Commonly found in volcanic regions like the Keweenaw Peninsula (Michigan), Iceland, and parts of India and Brazil.

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