igneous

Porphyritic Basalt (Chinese Writing Stone)

Porphyritic Basalt with Feldspar Phenocrysts

Hardness: 6-6.5 (Mohs); Color: Dark grey to black matrix with white or cream-colored crystals; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic matrix with lath-like phenocrysts; Cleavage: None in rock, perfect in feldspar crystals; Specific Gravity: 2.8-3.0

Hardness: 6-6
Luster: Dull to sub-vitreous

Identified April 5, 2026More igneous →

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Physical properties

Formation & geological history

Formed from rapid cooling of volcanic lava that began cooling slowly underground. This two-stage cooling process allows large crystals (phenocrysts) to form before the remaining magma erupts and cools quickly into a fine-grained matrix. Often associated with Mesozoic to Cenozoic volcanic activity.

Uses & applications

Used primarily as decorative stone, lapidary carvings, cabochons for jewelry, and as a unique collector's specimen. In larger quantities, basalt is used as crushed stone in construction.

Geological facts

Commonly known as 'Chinese Writing Stone' because the white feldspar crystals can resemble ancient calligraphy or characters against the dark background. It is chemically very similar to regular basalt but visually distinctive due to its texture.

Field identification & locations

Identify in the field by the 'porphyritic texture'—distinct white 'laths' or rectangular shapes embedded in a very fine-grained, dark, heavy rock. Commonly found in areas with past volcanic activity like California (USA) or British Columbia (Canada).

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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