igneous

Porphyritic Granite (Glacial Erratic)

Porphyritic Biotite Granite

Hardness: 6-7 Mohs; Color: Pinkish-red matrix with large black (hornblende/biotite) and white/grey (quartz) crystals; Luster: Dull to vitreous; Structure: Phaneritic/Porphyritic (visible large crystals); Specific Gravity: 2.6-2.7

Hardness: 6-7 Mohs
Luster: Dull to vitreous

Identified May 25, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep underground, often dating back to the Proterozoic or Archean eons. This specific specimen is likely a glacial erratic, transported far from its source by ice sheets during the last Ice Age.

Uses & applications

Used in high-end construction, kitchen countertops, monument carving, and as decorative landscaping boulders.

Geological facts

Granite is the primary component of continental crust. The pink color comes from potassium feldspar (orthoclase). This boulder is known as an 'erratic' because its composition differs from the local bedrock where it was deposited.

Field identification & locations

Identify by the 'salt and pepper' look with distinct pink feldspar crystals. Often found in glacial till or as solitary boulders in fields. Collectors look for unique phenocrysts (large crystals) and rounded weather patterns.

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

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral