igneous

Granite Glacial Erratic

Phaneritic Plutonic Felsic Rock (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8 – SiO2)

Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (mottled grey, white, and black). Luster: Dull (weathered) to vitreous (fresh break). Structure: Massive, phaneritic (visible coarse grains). Cleavage: Imperfect. Specific Gravity: 2.63 to 2.75.

Hardness: 6-7 on Mohs scale
Color: Salt-and-pepper (mottled grey, white, and black)
Luster: Dull (weathered) to vitreous (fresh break)

Identified March 22, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep underground (plutonic). This specific specimen appears to be a glacial erratic, transported by ice sheets during the Pleistocene epoch and rounded by glacial/fluvial abrasion.

Uses & applications

Used widely in construction for countertops, floor tiles, and paving stones. In its raw form, it is used for riprap, road base, and as decorative landscaping boulders.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Because it is so resistant to weathering, large boulders like this one can remain on the surface for thousands of years after being deposited by retreating glaciers.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and visible interlocking crystals of quartz, feldspar, and mica. It will not be scratched by a steel knife. Commonly found in mountainous regions or glacial till plains.

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Fluorapatite (Ca5(PO4)3F)

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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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

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Magnetite

Magnetite (Fe3O4)

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