Aventirine, a variety of quartz, and also one of feldspar. The peculiarity in each, for which the name is given, is the play of reflected or refracted light from numerous points in the mass of the stone - the reflections being bright and sparkling, and of different colors, while the ground may be translucent with little brilliancy, and of a dull color. The effect is probably produced by the crystalline faces in the structure of the stone refracting the light differently. There are, however, some varieties, called also aventurine, in which the play of colors results from the presence of numerous little scales of mica, or other foreign ingredients, each of which reflects the light, and all together produce a similar effect to that of the true varieties of aventurine. An artificial glass of this name is manufactured at Venice, which is well adapted to ornamental purposes, being even more beautiful than the natural minerals. Within the glass are substances apparently vitreous, of great brilliancy, of the color of copper, and in very small crystals of the form of tetrahedrons.
It is said to have been discovered by a workman in' Murano through accident (aventura) letting fall brass filings into molten glass.