igneous
Chinese Writing Stone
Porphyritic Basalt or Porphyritic Andesite
Hardness: 5-6 (Mohs scale); Color: Dark grey to greenish-black matrix with white or cream-colored crystals; Luster: Dull to vitreous; Crystal Structure: Large lath-shaped phenocrysts of plagioclase feldspar; Cleavage: Good in feldspar crystals.
- Hardness
- 5-6 (Mohs scale)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark grey to greenish-black matrix with white or cream-colored crystals; Luster: Dull to vitreous; Crystal Structure: Large lath-shaped phenocrysts of plagioclase feldspar; Cleavage: Good in feldspar crystals.
Formation & geological history
Formed from volcanic activity where magma cooled in two stages: first slowly deep underground to grow larger crystals (phenocrysts), and then rapidly upon eruption to form the fine-grained matrix. Often dates to the Mesozoic or Cenozoic eras.
Uses & applications
Primarily used as a decorative stone for lapidary work, including cabochons, carvings, beads, and polished display specimens.
Geological facts
The name comes from the white feldspar crystals which are often arranged in patterns resembling traditional Chinese calligraphy characters. While often found in China, significant deposits also exist in California, USA.
Field identification & locations
Identify by looking for distinct, needle-like or rectangular white crystals distributed randomly throughout a dark, fine-grained volcanic rock. Collectors often look for high contrast between the matrix and the crystals.
