igneous
Chinese Writing Stone
Porphyritic Basalt (or Andesite) with Feldspar inclusions
Hardness: 5-6 (Mohs); Color: Dark green/black matrix with white or cream inclusions; Luster: Dull to sub-vitreous; Structure: Porphyritic (fine-grained matrix with large crystals); Cleavage: None (rock mass); Specific Gravity: 2.7-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark green/black matrix with white or cream inclusions
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark green/black matrix with white or cream inclusions; Luster: Dull to sub-vitreous; Structure: Porphyritic (fine-grained matrix with large crystals); Cleavage: None (rock mass); Specific Gravity: 2.7-3.0
Formation & geological history
Formed through two-stage cooling of volcanic magma. Large plagioclase feldspar crystals (phenocrysts) formed slowly underground (Proterozoic to Mesozoic eras), followed by rapid surface cooling of the surrounding basaltic matrix during eruption.
Uses & applications
Primarily used for lapidary work including cabochons, carvings, and decorative tiles. It is popular in metaphysical circles and for ornamental jewelry.
Geological facts
Also known as 'Porphyry', it gets its name because the white crystals resemble Chinese characters or calligraphy marks. It is often confused with Snowflake Obsidian, but it is much harder and more durable.
Field identification & locations
Identify by looking for white, elongated lath-like crystals set against a dark, dense, fine-grained background. Found largely in the Yangtze River region of China and the foothills of the Sierra Nevada mountains in California. Collectors should look for high contrast between the 'ink' and the 'paper'.
