igneous
Banded Jasper / Rhyolite (Picture Jasper)
Silicified Rhyolitic Tuff / Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectMohs hardness 6.5-7; vitreous to waxy luster when polished; microcrystalline/cryptocrystalline texture; distinct sedimentary or flow banding in shades of green, cream, tan, and dark brown; specific gravity approximately 2.58-2.65.
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Physical properties
Mohs hardness 6.5-7; vitreous to waxy luster when polished; microcrystalline/cryptocrystalline texture; distinct sedimentary or flow banding in shades of green, cream, tan, and dark brown; specific gravity approximately 2.58-2.65.
Formation & geological history
Formed via silicification of volcanic ash or tuff, often associated with fine-grained rhyolitic volcanic eruptions. Silica-rich hydrothermal waters percolated through layered volcanic or sedimentary deposits, replacing the minerals and depositing varied mineral oxides that created distinct color bands.
Uses & applications
Commonly carved and polished into decorative shapes such as eggs, spheres, and cabochons for lapidary art, jewelry, and mineral collections.
Geological facts
Banded jaspers and silicified rhyolites (such as Wonderstone or Kambaba/polychrome types) get their distinct earthy bands from varying concentrations of iron oxides, hydroxides, and chlorite minerals deposited in rhythmic layers.
Field identification & locations
Identifiable by its dense microcrystalline nature, high polish, conchoidal fracture where broken, and distinct volcanic or sediment-like banding. Notable sources include Madagascar, Mexico, South Africa, and the western United States (e.g., Oregon and Idaho).
