mineral
Purple chalcedony / agate
Microcrystalline quartz (SiO₂), likely iron-stained chalcedony with possible amethystine coloration
AI-generated identification · may be incorrectTranslucent lavender-purple and tan-brown zones with a waxy to vitreous luster; irregular conchoidal fracture and no obvious cleavage. Mohs hardness about 6.5–7; specific gravity approximately 2.6. The rough surface appears partly weathered and may include quartz-rich matrix.
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Physical properties
Translucent lavender-purple and tan-brown zones with a waxy to vitreous luster; irregular conchoidal fracture and no obvious cleavage. Mohs hardness about 6.5–7; specific gravity approximately 2.6. The rough surface appears partly weathered and may include quartz-rich matrix.
Formation & geological history
Forms when silica-rich groundwater fills cavities and fractures, commonly in volcanic rocks; trace iron and other impurities create brown, purple, and reddish colors. Precise age cannot be determined visually; material in the Spokane region commonly relates to Tertiary volcanic rocks and younger gravels.
Uses & applications
Used for cabochons, beads, carvings, polished slabs, and ornamental stone; attractive translucent pieces have modest lapidary value.
Geological facts
The purple color may be natural amethystine quartz, iron-stained chalcedony, or enhancement; color alone cannot confirm amethyst. A close look for fine concentric or mossy banding would support an agate identification.
Field identification & locations
Likely plausible near 47.7°N, 117.4°W, where basalt-hosted silica veins, geodes, and transported agate/chalcedony occur. Test only on an inconspicuous edge: it should scratch glass but not be scratched by a steel knife; avoid destructive tests if collectible.
