igneous
Wonderstone (Banded Rhyolite)
Rhyolite (Silicon Dioxide with Iron Oxide impurities)
Hardness: 6-7 on Mohs scale; Color: Red, tan, cream, and grey bands; Luster: Matte to earthy (waxy when polished); Crystal Structure: Aphanitic (fine-grained) to glassy; Cleavage: None (conchoidal fracture).
- Hardness
- 6-7 on Mohs scale
- Color
- Red, tan, cream, and grey bands
- Luster
- Matte to earthy (waxy when polished)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Red, tan, cream, and grey bands; Luster: Matte to earthy (waxy when polished); Crystal Structure: Aphanitic (fine-grained) to glassy; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed from volcanic eruptions where thick, silica-rich lava cools quickly. The distinct banding is caused by the flow of the lava and the oxidation of iron-bearing minerals (hematite or goethite) within the rock layers, often dated to the Tertiary period.
Uses & applications
Primarily used for ornamental purposes, lapidary work (cabochons, beads), decorative garden stones, and as a popular specimen for collectors due to its unique patterns.
Geological facts
Wonderstone is famous for its 'painterly' look, which can resemble desert landscapes. While it looks like sedimentary sandstone because of the bands, it is actually a hard volcanic rock that can take a high polish.
Field identification & locations
Identify in the field by its distinct colorful banding and its hardness (it will scratch glass, unlike similar-looking sandstone). Common locations include Nevada and Utah in the USA, and parts of South Africa.
