igneous

Greenstone Porphyry

Porphyritic Metavolcanic Rock

Hardness: 6-7 (Mohs); Color: Dark green matrix with greenish-white or pinkish feldspar phenocrysts; Luster: Dull to sub-vitreous; Structure: Massive with porphyritic texture; Cleavage: None (conchoidal fracture).

Hardness: 6-7 (Mohs)
Luster: Dull to sub-vitreous

Identified May 8, 2026More igneous →

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Physical properties

Formation & geological history

Formed from volcanic eruptions where magma cooled at two different rates, creating large crystals (phenocrysts) in a fine-grained matrix. Often metamorphosed over millions of years (Greenschist facies), common in Precambrian and Paleozoic terrains.

Uses & applications

Used as high-quality building stone, decorative landscaping, and historically for stone tools due to toughness. Occasionally used in jewelry as 'Green Porphyry'.

Geological facts

The 'Green Porphyry' specifically from Greece (Lapis Lacedaemonius) was highly prized by Roman emperors and used in the Pantheon and the Church of Hagia Sophia.

Field identification & locations

Identify by the distinct 'spotted' appearance of large crystals embedded in a uniform green background. Often found as rounded river stones or glacial erratics in the Northern US and Europe.

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