Blue Aventurine

India is by far the most important commercial producer of aventurine and Brazil is second; smaller amounts come from Russia, Spain, Austria and Tanzania. Aventurine is a variety of quartzite, a metamorphic rock formed when quartz sandstone or chert recrystallizes into a tight network of quartz grains. Geology.com illustrates blue aventurescent quartz from India. Blue dumortierite quartzites used as ornamental stone are also mined in Brazil, Mozambique and Madagascar.

Natural blue colour in quartz rock can look like dye. In one Gems & Gemology report, a blue dumortierite-quartz rock submitted as sapphire showed blue concentrated between white quartz grains, as in dyed material, but reflected light revealed blue dumortierite grains with a different luster, the specific gravity was 2.99 (quartz is about 2.65), and Raman analysis confirmed dumortierite and quartz. By contrast, blue beads that GIA reported as composites of dyed quartzite pieces held in polymer showed dye in their many fractures, a red reaction under the Chelsea filter and a band near 650 nm in the spectroscope. Dyeing of quartz is common and dye concentrations can be seen with magnification.

Aventurine has the hardness of quartz (6.5 to 7), but abundant mica can lower its apparent hardness and give it a direction of easier breakage, and coarse mica flakes can pluck out of a polished surface and leave pits. IGS lists no special care for quartz, but notes that some dyes used on quartz fade, which matters for the oiled or dyed beads that are common in the trade.

Mindat derives the name from the Italian "a ventura", meaning "by chance", and links it to aventurine glass, a glittering glass with copper inclusions first made in Italy. Mindat also notes that "aventurine" is used commercially for several kinds of stones, including aventurine feldspar (sunstone); the natural quartz material is also called aventurine quartz and is not to be confused with aventurine glass (goldstone).

The Japanese retailer Pascle writes that blue aventurine, like green aventurine, is said to ease stress and tension, and that it is believed to calm the emotions and soften anxiety.