igneous

Granite Pebble

Granite (composed primarily of Quartz: SiO2, Feldspar: KAlSi3O8, and Mica: K(Mg,Fe)3AlSi3O10(OH)2)

Hardness: 6-7 Mohs; Color: Light gray, tan, or salt-and-pepper appearance; Luster: Vitreous to dull; Structure: Phaneritic (medium-grained crystalline); Cleavage: Irregular fracture in mass

Hardness: 6-7 Mohs
Color: Light gray, tan, or salt-and-pepper appearance
Luster: Vitreous to dull

Identified May 29, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: Light gray, tan, or salt-and-pepper appearance; Luster: Vitreous to dull; Structure: Phaneritic (medium-grained crystalline); Cleavage: Irregular fracture in mass

Formation & geological history

Formed from the slow cooling of magma beneath the Earth's surface (intrusive). This specific pebble was later rounded by water/erosion in a riverbed or coastal environment.

Uses & applications

Commonly used in large scale for construction, countertops, and road base. In pebble form, used for landscaping and decorative garden features.

Geological facts

Granite makes up much of the Earth's continental crust; it is incredibly durable and resistant to acid, which is why it occupies such high importance in architecture.

Field identification & locations

Identify in the field by its speckled 'salt and pepper' appearance and its inability to be scratched by a steel pocketknife. Found globally in mountainous or glaciated regions.

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

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

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