The chemistry behind precious jewels
In terms of chemical composition, opal is an amorphous variety of silica. In other words, it contains some water inside, which makes it sensitive to cracking and crazing. Being one of quartz varieties, opals form small spheres that amaze spectators.
The most common opals have milky or pure white hue. However, other opals are also valuable. In the group of black opals, Australia’s Lightning Ridge is a top pick. This dry and rocky region creates the best circumstances for an opal to appear.
When it comes to tourmaline, it's crystalline boron silicate mineral chemically. This special jewel can demonstrate a “cat’s eye” effect or be painted by chromium. Also, the most common types are Indicolite, Paraiba, Rubellite, and Schorl.