igneous
Dalmation Stone
Peralkaline rhyolite (SiO2 with Arfvedsonite/Riebeckite)
Hardness: 5-7.5 (Mohs scale), Color: Creamy white with black spots, Luster: Vitreous to dull, Crystal structure: Microcrystalline, Cleavage: None, Specific gravity: 2.6-2.7
- Hardness
- 5-7
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Physical properties
Hardness: 5-7.5 (Mohs scale), Color: Creamy white with black spots, Luster: Vitreous to dull, Crystal structure: Microcrystalline, Cleavage: None, Specific gravity: 2.6-2.7
Formation & geological history
Formed from the rapid cooling of silica-rich volcanic lava, where black spots of arfvedsonite or other amphiboles crystallize within a microcrystalline quartz and feldspar matrix.
Uses & applications
Primarily used for decorative purposes, lapidary arts, beads for jewelry, and as pocket stones or carvings for collectors.
Geological facts
Despite being called 'Dalmatian Jasper' in the trade, it is technically an igneous rock (rhyolite), not a true sedimentary jasper. The black spots were long thought to be tourmaline but are actually arfvedsonite.
Field identification & locations
Identify by its distinctive black-on-white 'polka dot' pattern and hardness. It is notoriously found in Chihuahua, Mexico. Collectors should look for a smooth, uniform surface without surface pits.
