igneous

Granitoid (Granite/Diorite)

Course-grained Plutonic Igneous Rock

Hardness: 6-7 Mohs; Color: Salt and pepper (mottled grey, black, and tan); Luster: Dull to vitreous; Structure: Phaneritic (visible crystals); Cleavage: Distinct in feldspar grains; Specific gravity: ~2.6-2.8

Hardness: 6-7 Mohs
Color: Salt and pepper (mottled grey, black, and tan)
Luster: Dull to vitreous

Identified May 16, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling and crystallization of magma deep beneath the Earth's surface (plutonic formation). This specimen shows rounding and smoothing, indicating it was likely transported by water in a river or coastal environment.

Uses & applications

Used widely in construction as crushed stone, dimension stone for countertops and flooring, and occasionally in landscaping as river rock.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Because it cools slowly underground, individual mineral crystals such as quartz, feldspars, and micas have time to grow large enough to be seen with the naked eye.

Field identification & locations

Identify by its interlocking 'salt and pepper' crystalline texture and extreme hardness (cannot be scratched by a steel knife). Commonly found in mountain ranges and as rounded cobbles in glacial till or riverbeds.

Other igneous specimens

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Blue Apatite

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)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral