igneous
Chinese Writing Stone
Porphyritic Basalt or Porphyritic Andesite
Hardness: 5-6 (Mohs scale); Color: Dark green to black groundmass with cream to light green needle-like crystals; Luster: Dull to sub-vitreous; Crystal Structure: Porphyritic (fine-grained matrix with large inclusions); Cleavage: None (conchoidal fracture).
- Hardness
- 5-6 (Mohs scale)
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark green to black groundmass with cream to light green needle-like crystals; Luster: Dull to sub-vitreous; Crystal Structure: Porphyritic (fine-grained matrix with large inclusions); Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from volcanic activity where magma cooled in two stages: first slowly deep underground to form large phenocrysts, then rapidly at or near the surface to form the fine-grained matrix. Often associated with the Permian period (250-300 million years ago).
Uses & applications
Primarily used for lapidary work including cabochons, beads, and decorative carvings. Highly valued by crystal collectors for aesthetic beauty and use in metaphysical practices.
Geological facts
The name comes from the distinct needle-like andalusite or feldspar crystals that resemble Chinese calligraphy characters. While often found in China, high-quality specimens are also frequently sourced from the foothills of the Sierra Nevada mountains in California.
Field identification & locations
Identify by looking for the contrast between a very dark basaltic background and lighter, geometric, elongated crystal clusters. It is commonly found in riverbeds or mountain ranges with high volcanic history. Collectors should look for distinct, sharp crystal 'strokes'.
