igneous

Granodiorite Pebble

Granodiorite (containing Quartz, Plagioclase Feldspar, and Biotite/Amphibole)

Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (white, gray, and black). Luster: Dull to vitreous. Crystal structure: Phaneritic (medium-grained crystalline). Cleavage: Varies by mineral constituent. Specific gravity: 2.6-2.7.

Hardness: 6-7 on Mohs scale
Color: Salt-and-pepper (white, gray, and black)
Luster: Dull to vitreous

Identified March 24, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma beneath the Earth's surface (intrusive). The rounded shape indicates secondary erosion and transport by water in a river or coastal environment.

Uses & applications

Commonly used as crushed stone for road construction, building materials, and as decorative landscaping stones. Higher quality slabs are used for countertops similarly to granite.

Geological facts

Granodiorite is the intermediate rock between granite and diorite. The famous Rosetta Stone was carved from a slab of granodiorite, though it was originally misidentified as basalt.

Field identification & locations

Identify by its 'salt and pepper' appearance and visible crystalline texture. It is harder than steel and will scratch glass. Found globally in batholiths and eroded mountain ranges, often appearing as smooth cobbles in stream beds.

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)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral