Catalog Search Guide
You can search our catalog using different mineral attributes. For example, you can search by color such as green, yellow or purple, or by chemical elements such as uranium, calcium or iron, or by mineral groups such as phosphate, silicate or carbonate. You can also filter by crystal habit like crystal, geode or crystal on matrix, by specimen size such as thumbnail, small, medium or cabinet, and by features such as radioactive or fluorescent minerals.
Hyalite
Hyalite is a colorless, glassy variety of common opal (Opal-AN), an amorphous hydrous silica prized for its clear, jelly-like botryoidal and globular crusts rather than any play-of-color. Unlike precious opal, hyalite lacks internal diffraction structure, but many specimens compensate with a striking party trick: a bright green fluorescence under both shortwave and longwave UV, and in the finest material even a visible daylight glow. This luminescence comes from trace amounts of the uranyl (UO2)2+ molecule locked into the silica gel as it deposited from volcanic or pegmatitic vapors, giving hyalite a devoted following among fluorescent mineral collectors alongside classics like autunite and adamite.
Historically the type material comes from the volcanic clefts of Valeč in the Karlovy Vary Region of the Czech Republic, a locality so significant that hyalite from trachytic rocks there and in the Auvergne region of France defined the variety for 19th-century mineralogists. Classic European hyalite is also documented from Hungary and from pegmatite pockets such as the Naegi granite in Gifu, Japan, and hot-spring deposits at Toyama's Shin-yu locality. Additional occurrences are known from Oregon and Utah in the United States, from Ararat in Turkey, and from widespread but poorly documented finds across Argentina.
The specimens that revolutionized the hyalite market, however, came from Zacatecas, Mexico, first found around 2013 at the so-called Electric Opal claim. This Mexican hyalite shows an intensely bright yellow-green glow under UV and, remarkably, a visible green fluorescence in ordinary shaded daylight — a phenomenon almost unmatched among fluorescent minerals and shared by only a handful of other deposits, notably in the Erongo region of Namibia. Trace uranium content makes these pieces mildly radioactive, though at levels well below any health concern. Because true daylight-fluorescent hyalite is genuinely scarce on the specimen market, well-formed botryoidal clusters with strong green response — whether from Zacatecas, Erongo, or the historic Czech and Hungarian deposits — remain highly sought after by opal specialists, UV-mineral collectors, and anyone assembling a representative silica-mineral suite.
