igneous

Porfido (Porphyritic Rock)

Porphyry (often Rhyolitic or Andesitic)

Hardness: 6-7 on Mohs scale; Color: Reddish-brown or purple groundmass with white or cream inclusions; Luster: Dull to sub-vitreous (when polished); Texture: Porphyritic (fine-grained matrix with larger visible crystals); Specific Gravity: 2.6-2.8.

Hardness: 6-7 on Mohs scale
Luster: Dull to sub-vitreous (when polished)

Identified April 4, 2026More igneous →

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Physical properties

Formation & geological history

Formed from volcanic activity when magma experiences two stages of cooling: a slow stage underground creating large crystals (phenocrysts), followed by rapid cooling upon eruption or shallow intrusion forming the fine-grained matrix.

Uses & applications

Used widely in decorative landscaping, street paving (cobblestones), interior floor tiles, wall cladding, and as an ornamental stone in jewelry or tumbled stone collections.

Geological facts

The word Porphyry comes from the Greek word for 'purple.' Imperial Porphyry from Egypt was once more valuable than gold and was used exclusively for Roman emperors' thrones, statues, and sarcophagi due to its royal color.

Field identification & locations

Identified by the distinct contrast between the fine-grained base and the 'speckled' larger crystals. Commonly found in regions with volcanic history like Italy, Egypt, Mexico, and the Southwestern US. Collectors look for high contrast and color saturation.

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