igneous

Porphyritic Basalt (Chinese Writing Stone)

Porphyritic Basalt with Feldspar Phenocrysts

Hardness: 6-7 (Mohs); Color: Dark grey or black matrix with white or cream needle-like inclusions; Luster: Dull to sub-vitreous; Crystal structure: Orthorhombic/Triclinic phenocrysts; Cleavage: None (matrix); Specific gravity: 2.8-3.0

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

Identified June 2, 2026More igneous →

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Physical properties

Formation & geological history

Formed from cooling lava where crystals (usually plagioclase feldspar) began to grow slowly underground before the remaining magma erupted and cooled quickly on the surface, trapping the larger crystals in a fine-grained matrix. Common in volcanic regions including California and parts of Asia.

Uses & applications

Used primarily as a decorative stone, for lapidary work like cabochons, carvings, and as a unique collector's specimen due to its calligraphy-like appearance.

Geological facts

The nickname 'Chinese Writing Stone' comes from the random orientation of the feldspar crystals which look like ancient Chinese script or petroglyphs. It is also sometimes referred to as 'Porphyry'.

Field identification & locations

Identified by the distinct lath-shaped or needle-like light colored crystals set against a dark, dense, fine-grained background. Commonly found in riverbeds or coastal areas near former volcanic activity. Collectors look for high contrast between the 'letters' and the matrix.

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Dark Igneous Rock (Likely Basalt or Diabase)

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