igneous
Porphyritic Basalt (Chinese Writing Stone)
Porphyritic Basalt with Feldspar phenocrysts
Hardness: 6-7 (Mohs scale), Color: Dark greenish-grey to black groundmass with white/cream inclusions, Luster: Dull to sub-vitreous, Crystal structure: Aphanitic (fine-grained) matrix with large tabular crystals (phenocrysts).
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark greenish-grey to black groundmass with white/cream inclusions, Luster: Dull to sub-vitreous, Crystal structure: Aphanitic (fine-grained) matrix with large tabular crystals (phenocrysts).
Formation & geological history
Formed through two stages of cooling: first, large crystals of feldspar grew slowly within magma underground, followed by a rapid eruption where the remaining liquid cooled quickly into a fine-grained matrix.
Uses & applications
Used primarily for lapidary work, decorative carvings, landscaping, and as a unique collector specimen for its aesthetic patterns.
Geological facts
Commonly referred to as 'Chinese Writing Rock' or 'Llanite' (though true Llanite is rhyolitic), the name comes from the white feldspar crystals resembling ancient calligraphy characters.
Field identification & locations
Identify by looking for white, elongated 'laths' of feldspar embedded in a dark, hard volcanic matrix. Often found in riverbeds or coastal areas where volcanic activity occurred, particularly in regions like California or Nevada.
