igneous
Porphyritic Basalt (Chinese Writing Stone)
Porphyritic Basalt or Andesite containing plagioclase feldspar phenocrysts
Hardness: 6-7 on Mohs scale. Color: Dark grey to black matrix with white or cream-colored patterns. Luster: Dull to vitreous when polished. Crystal structure: Porphyritic texture with larger crystals (phenocrysts) in a fine-grained groundmass.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to vitreous when polished
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark grey to black matrix with white or cream-colored patterns. Luster: Dull to vitreous when polished. Crystal structure: Porphyritic texture with larger crystals (phenocrysts) in a fine-grained groundmass.
Formation & geological history
Formed from volcanic activity where magma cooled slowly underground to create larger crystals, then quickly at the surface to form the fine-grained matrix. Found often in California (USA) and portions of China.
Uses & applications
Primarily used for lapidary work including cabochons, beads, decorative carvings, and garden ornaments due to its unique pattern.
Geological facts
The name 'Chinese Writing Stone' is a trade name based on the crystal patterns resembling various characters of Chinese calligraphy. It is often chemically related to Basalts or Rhyolites.
Field identification & locations
Look for a dark, hard volcanic rock containing light-colored, elongated lath-like crystals. It is frequently found as river-worn pebbles in specific geological zones near volcanic deposits.
