igneous

Diorite (or salt-and-pepper granite pebble)

Phaneritic Igneous Rock (Intermediate Composition)

Hardness: 6-7 Mohs; Color: Mottled black and white (speckled); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained visible crystals); Clearing: Good in two directions (feldspars).

Hardness: 6-7 Mohs
Color: Mottled black and white (speckled)
Luster: Sub-vitreous to dull

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of magma deep beneath the Earth's surface (intrusive). Commonly associated with volcanic arcs and subduction zones. This specimen appears water-worn, indicating it was transported by a river or glacier.

Uses & applications

Larger deposits are used for construction as crushed stone, floor tiles, and countertop material. Polished pebbles are used in decorative landscaping and aquarium gravel.

Geological facts

Diorite is often referred to as 'salt and pepper' rock due to its distinctive color mix. It was used by ancient civilizations, such as the Egyptians and Sumerians, for high-quality statues because of its extreme hardness.

Field identification & locations

Identify by looking for a 'salt and pepper' appearance with crystals of roughly equal size (no visible quartz usually separates it from granite). It is commonly found in mountain ranges and glacial deposits near ancient igneous activity.

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

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral