Aventurine

What is aventurine?

Source: tatoeba (7128610)

[pages 244–245] Aventurine is a brown glass flux, containing very small glittering particles, which give it a peculiarly glittering appearance. It was formerly manufactured into objects of art and ornament at Murano near Venice. [...] The statements which are found respecting it in technological works, according to which it is obtained by fusing down with glass minute particles of gold, copper, brass, mica, or talc, are not correct, as the microscopic examination of aventurine plainly shows. [page 246] There can be no doubt therefore that the crystals in the aventurine consist of metallic copper, which were separated in a crystalline state from the fused glass containing oxide of copper by the addition of some reducing substance.

Source: wiktionary

With 40 grms. of the bichromate, the fusion is decidedly more difficult, and the glass is filled with extremely brilliant crystals. Those persons who saw specimens of this glass, at once compared it to Venetian aventurine, and called it chrome aventurine, which name I propose to retain. [...] Chrome aventurine sparkles in the sun and in strongly lighted places; in this respect it is surpassed by diamond alone. It is harder than common glass, which it scratches and cuts easily, and is especially harder than the Venetian aventurine; hence its greater value.

Source: wiktionary

Aventurin or avanturin glass was formerly made only in the Island of Murano, near Venice, but is now prepared throughout Germany, Italy, Austria, and France. It is a brown glass mass in which crystalline spangles of metallic copper according to [Friedrich] Wöhler (of protoxide of copper according to [Max Joseph] von Pettenkofer) appear dispersed. [...] The Bavarian and Bohemian glass-houses produce an aventurin glass rivalling the original.

Source: wiktionary