igneous

Basalt-Amugydule (Amygdaloidal Basalt)

Aphanitic Mafic Igneous Rock with Vesicle Infillings

Hardness: 5-6 (the host basalt), Color: dark grey to black matrix with light-colored mineral pockets, Luster: dull for the matrix, vitreous for infusions, Crystal structure: microcrystalline, Cleavage: none.

Identified April 4, 2026More igneous →

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Physical properties

Formation & geological history

Formed from cooling lava flows where gas bubbles (vesicles) were trapped. Over geological time, groundwater filled these holes with minerals like quartz, calcite, or zeolites. Can date from various volcanic eras across hundreds of millions of years.

Uses & applications

Used in construction as crushed stone or aggregate. High-quality specimens with colorful agate or amethyst infillings are used for jewelry or as decorative collection pieces.

Geological facts

The holes are called 'vesicles' when empty and 'amygdules' (from the Greek for almond) when they are filled with secondary minerals.

Field identification & locations

Identify by the dark, heavy matrix with distinct 'spots' of different minerals. Commonly found in old volcanic regions like the Lake Superior area, Oregon, or Ireland.

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