igneous

Porphyritic Basalt (Chinese Writing Stone)

Porphyritic Basalt with Feldspar Phenocrysts

Hardness: 6-7 (Mohs); Color: Dark grey to black groundmass with white/pale grey laths; Luster: Dull to sub-vitreous; Crystal structure: Porphyritic (fine-grained matrix with larger visible crystals); Cleavage: Indistinct; Specific Gravity: 2.8-3.0.

Hardness: 6-7 (Mohs)
Color: Dark grey to black groundmass with white/pale grey laths
Luster: Dull to sub-vitreous

Identified April 7, 2026More igneous →

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Physical properties

Formation & geological history

Formed from volcanic lava cooling in two stages: slow cooling at depth allowed large crystals (phenocrysts) to form, followed by rapid cooling at the surface forming the fine-grained matrix. Found in Cenozoic volcanic regions.

Uses & applications

Primarily used as a decorative stone, for lapidary work (cabochons), and in ornamental carvings or architectural accents.

Geological facts

The name 'Chinese Writing Stone' (or Basalt) comes from the needle-like crystals of feldspar that resemble traditional Chinese characters or calligraphy marks.

Field identification & locations

Identify by the distinct 'matchstick' or calligraphic pattern of light crystals against a dark background. Commonly found in California (USA), Canada, and Asia near anciennes volcanic flows.

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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)

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Magnetite

Magnetite (Fe3O4)

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