AVANTURINE, a mineral which is found variously coloured and always enclosing particles of mica; the most common colour of the base is brown or reddish brown. It is worked by the lapidary like Carnelian, but does not admit of so good a polish as the imitation.

2. - Factitious Avanturine, which is glass or paste enclosing particles of metal is generally more close and brilliant than the real stone, and was much used in common jewellery, the imitation avanturine is cut and polished like other pastes, as described under the head Alabaster, article 3. The method of making this artificial avanturine which is now lost, is considered to have originated with the Italian artists, this substance is now very scarce and much valued.

3. - Artificial Avanturine which is more brilliant than the last, and used as a microscopic object, is prepared from blue glass coloured by the oxide of copper, which is stirred with an iron rod. The oxygen from its superior affinity for the latter metal quits the copper, and unites itself to the iron, and in the act of resuming the metallic form, the copper partially crystallizes, and becomes entangled in the glass. From the striated condition the glass assumes on being stirred, the bright and metallic picture is irregular, and appears full of hills and dales, occasionally clouded with the dark coloured glass in which no copper is visible. The crystallization may be distinctly seen with a common lens of half an inch focus.