igneous
Wonderstone
Banded Rhyolite (SiO2 with impurities)
Hardness: 6-7 (Mohs scale), Color: Cream, tan, red, pink, and purple bands, Luster: Dull to earthy (waxy when polished), Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.4-2.6
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Cream, tan, red, pink, and purple bands, Luster: Dull to earthy (waxy when polished), Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.4-2.6
Formation & geological history
Formed during the Tertiary period (roughly 12-25 million years ago) from volcanic ash falls that were later compressed, welded by heat, and stained by groundwaters rich in iron and manganese oxides.
Uses & applications
Primarily used for lapidary work, including cabochons, bookends, or carvings. It is popular with hobbyists for tumbling and as decorative landscaping stone.
Geological facts
Wonderstone is a specific type of rhyolite tuff. The beautiful 'painting-like' bands are Liesegang rings, formed by the rhythmic precipitation of minerals from fluids moving through the porous volcanic rock.
Field identification & locations
Identify in the field by its distinct colorful banding and smooth, fine-grained texture. It is famously found in the Vernon Hills of Utah and near Fallon, Nevada. It does not react to acid.
