igneous
Wonderstone
Rhyolite (Silicon Dioxide with Iron Oxide impurities)
Hardness: 6-7 (Mohs scale), Color: Cream, tan, pink, and burgundy bands, Luster: Dull to earthy (unpolished) / Vitreous (polished), Crystal structure: Cryptocrystalline/Glassy matrix, Cleavage: None/Conchoidal fracture, Specific gravity: 2.4 - 2.6
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Cream, tan, pink, and burgundy bands, Luster: Dull to earthy (unpolished) / Vitreous (polished), Crystal structure: Cryptocrystalline/Glassy matrix, Cleavage: None/Conchoidal fracture, Specific gravity: 2.4 - 2.6
Formation & geological history
Formed from volcanic ash falls or rhyolitic flows during the Tertiary period (roughly 12-25 million years ago). The distinct banding is caused by the movement of mineral-rich groundwater (Liesegang rings) depositing iron oxides after the rock solidified.
Uses & applications
Used primarily for lapidary work including cabochons, carvings, and bookends. It is also used in decorative landscaping and as an ornamental collector's specimen.
Geological facts
The rhythmic banding is a chemical phenomenon called Liesegang rings. While it looks like sedimentary sandstone, it is actually a volcanic rock (rhyolitic tuff). The most famous deposits are found in the Vernon Hills of Utah.
Field identification & locations
Identify by its distinctive smooth, almost 'soapy' or fine-grained texture combined with concentric or wavy reddish-brown bands. Found primarily in arid volcanic regions of the Western United States like Utah, Nevada, and Arizona.
