igneous

Diorite (with Iron Staining)

Phaneritic Intermediate Igneous Rock

Hardness: 6-7 (Mohs scale); Color: Salt-and-pepper (white plagioclase, black hornblende/biotite) with reddish-brown iron oxide staining; Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained); Cleavage: Good in two directions via feldspar components; Specific Gravity: 2.8-3.0.

Hardness: 6-7 (Mohs scale)
Luster: Dull to sub-vitreous

Identified March 30, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow cooling of magma deep beneath the Earth's surface (intrusive) in volcanic arcs or subduction zones. The reddish staining on this specimen indicates secondary weathering where iron-bearing minerals have oxidized into limonite or goethite.

Uses & applications

Commonly used as a base material in construction, road building (crushed stone), and occasionally as a polished dimension stone for countertops or monuments. Historically used by ancient civilizations for sculpture due to its durability.

Geological facts

Diorite was used in ancient Egypt and Mesopotamia for crafting important monuments, including the famous Code of Hammurabi stele, because it is extremely tough and resists weathering better than marble.

Field identification & locations

Identify in the field by the distinct 'salt and pepper' appearance of interlocking crystals larger than 1mm. This specimen shows heavy surface oxidation. Commonly found in mountainous regions near plate boundaries like the Andes or the Cascades.

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

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Magnetite

Magnetite (Fe3O4)

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