Hyalite from Valeč, Bohemia – Glass Opal on Matrix

This Hyalite specimen from Valeč in Bohemia, Czech Republic, shows several rounded to botryoidal glass-opal aggregates on a dark, porous matrix. Particularly striking are the colorless to whitish Hyalite areas, which stand out clearly from the matrix due to their glassy surface and partly high light transmission.

Measuring 7.3 × 6.5 × 2.5 cm and weighing 188.3 g, this is a cabinet specimen. In addition to the colorless Hyalite areas, yellowish to ochre-colored parts occur locally, giving the specimen an interesting color variation within the same opal mineralization. The back of the specimen has been sawn, and the piece is glued to a small acrylic stand.

Glassy Hyalite with varying transparency

The Hyalite forms rounded to botryoidal aggregates with a distinctly glassy luster. The colorless areas are translucent to transparent and therefore show the water-clear to glass-like character typical of Hyalite particularly well.

Yellow to ochre-colored areas also occur. On this specimen, these parts are opaque and differ clearly from the more transparent Hyalite aggregates.

The combination of transparent to translucent colorless Hyalite and opaque ochre-colored areas shows several optical varieties of the mineral within a single specimen.

Hyalite from Valeč in Bohemia

Valeč in Bohemia is a classic locality for Hyalite and glass opal. The locality has long been known for rounded to botryoidal opal formations on volcanic rock.

Hyalite is a colorless to weakly colored variety of Opal characterized by its glassy luster and, in some areas, high transparency. Its occurrence on dark matrix often creates a particularly strong contrast.

This specimen is especially notable for the larger clear Hyalite aggregates and the combination of colorless and yellowish-ochre areas. The dark matrix further emphasizes the glassy character of the Opal. The sawn back and the small acrylic stand also provide stable presentation of the specimen.