igneous
Chinese Writing Stone
Porphyritic Basalt or Porphyritic Andesite with Feldspar phenocrysts (SiO2-rich Silicates)
Hardness: 5-6 (Mohs); Color: Black or dark olive green background with white or cream-colored patterns; Luster: Vitreous to dull; Crystal structure: Orthorhombic or Monoclinic phenocrysts in an aphanitic matrix; Cleavage: Visible in the white inclusions.
- Hardness
- 5-6 (Mohs)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 5-6 (Mohs); Color: Black or dark olive green background with white or cream-colored patterns; Luster: Vitreous to dull; Crystal structure: Orthorhombic or Monoclinic phenocrysts in an aphanitic matrix; Cleavage: Visible in the white inclusions.
Formation & geological history
Formed through volcanic activity where lava containing dissolved minerals cools slowly at depth (allowing large white crystals to form) and then erupts or moves to a cooler area to solidify rapidly (forming the dark matrix). Most specimens date back to the Permian era, approximately 250-290 million years ago.
Uses & applications
Primarily used for lapidary work, including cabochons for jewelry, tumbled stones, decorative carvings, and as a collector's specimen due to its unique aesthetics.
Geological facts
Its name comes from the white inclusions which often resemble Chinese calligraphy or characters. It is frequently confused with 'Turritella Agate' or 'Graphite Stone,' but it is actually a volcanic rock with feldspar laths.
Field identification & locations
Identify by looking for white, needle-like or blocky inclusions (phenocrysts) contrasting sharply against a very dark, fine-grained volcanic background. It is most famously found in the Yangtze River Valley in China and also in parts of California (Auburn) and Nevada.
