igneous

Granite Pebble

Granite (composition of Quartz, Alkali Feldspar, and Plagioclase)

Hardness: 6-7 Mohs; Color: Mottled gray, pink, white, and black; Luster: Vitreous to dull; Crystal Structure: Phaneritic (visible crystals); Cleavage: Feldspars show two planes at 90 degrees; Specific Gravity: 2.63-2.75

Hardness: 6-7 Mohs
Color: Mottled gray, pink, white, and black
Luster: Vitreous to dull

Identified May 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow crystallization of magma below Earth's surface. High in silica and alkali metal oxides. This specimen has been rounded by water erosion (alluvial/river action).

Uses & applications

Used in construction, countertops, monuments, and as decorative gravel or river rock for landscaping.

Geological facts

Granite is the primary constituent of Earth's continental crust. Over 80% of Earth's granite is found in the continental plates rather than the oceanic basins.

Field identification & locations

Identify by its 'salt and pepper' appearance and hardness (cannot be scratched by steel). Found globally in mountain ranges and riverbeds. Look for quartz (translucent) and feldspar (colored opaque) minerals.

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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 - 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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