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
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Physical properties
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
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.
