The name aventurine is applied to an ornamental material consisting mainly of quartz. It is therefore described here under this heading, although it is actually a metamorphic rock, a quartzite, containing platelike crystals of other minerals, usually green mica. It is also, improperly, called Indian jade. lt should not be confused with aventurine feldspar, a red variety of albite.

Appearance Consisting as it does of minute, juxtaposed grains, it is normally not transparent, but somewhat turbid. Sometimes the green mica plates are obvious and greatly influence the color, which may be an attractive, bright green. More often, it is merely greenish off-white or grayish white. The overall appearance can be quite similar to that of some jadeite.

It is generally cut into curved pieces for necklaces or other jewels, or for use as pendants, but is also much used for carving and figurines. Because of its heterogeneous structure, it does not easily acquire a good polish.

Distinctive features The granular appearance, the possible presence of distinct green fibers, and its particular translucence are the most distinctive characteristics. Specimens similar to jadeite jade are immediately distinguished by their density. It is also much more brittle-than jade.

Occurrence Aventurine comes mainly from India. Soviet Union, Brazil and Australia, but also from Germany It is also fashioned in all these countries.

Value Very modest, when, as is usually the case, the material is whitish to grayish or dull green and the workmanship is of a low level. But expertly fashioned, bright green pieces are almost as valuable as true jades.

Simulants and synthetics Aventurine feldspar is imitated by glass, usually in the form of a brown paste containing golden metallic fibers, hence somewhat dissimilar Some people, in fact, claim that the name aventurine war originally given to a type of Murano glass containing metalIic fibers and only subsequently applied to the ornamental mineral which looks (very vaguely) like it. It is not manufactured synthetically. Because of its granular structure minute discontinuities and porosity, aventurine absorbs artificial colorants quite easily, and consequently it is sometimes given a bright green color, with a view to greatly increasing its value.