Aventurine

[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.

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.

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.

The Sandaresus, an Arabian stone, classed by Pliny [the Elder] among the Carbunculi, seems to have been our Aventurine, for he describes it as full of golden stars shining through a transparent substance, not from the surface, but from within the body of the stone. The true Aventurine, or Goldie-stone, is a brownish semi-transparent quartz, full of specks of yellow mica.

Aventurine is a variety of grainy quartz,—not quarts of rye whiskey, which there is too much of a venture in,—but quartz of silica, gold-spangled throughout with flakes of yellow mica. [...] There are two kinds of natural aventurine; the one with its spangles of yellow mica is well known as Muscovite talc. It was found on the shores of the White Sea in old times, and is now met with often in the mines of Silesia, in Bohemia, in France, and in Siberia. The other variety, more highly esteemed, is found in Spain and in Scotland. [...] Dealers have given the name of aventurine to a species of feldspar having the same external characteristics, and sold for the genuine, though a much softer stone. Such dealers are not honest.

[F]rom out the silken curtain-folds / Bare-footed and bare-headed three fair girls / In gilt and rosy raiment came: their feet / In dewy grasses glisten'd; and the hair / All over glanced with dewdrop or with gem / Like sparkles in the stone Avanturine.

During this period of two centuries little colour was employed in the lacquer-work, but much gold was used; and those particular kinds of work in which "clouded" gold effects, avanturines, and tesselated gold are introduced, as well as low-relief modelling of a most perfect kind, were invented and brought to a high state of perfection.

Quartz with spangled inclusions is known as aventurine. The included minerals are scales of shiny mica or hematite. The most familiar aventurine is of a reddish-yellow color and has a coppery sheen. Only small quantities of aventurine have been found in the United States.