I've been thinking that I might make some notes about some of the stones I work with and my experiences working with them. I figured I would start with an A - apatite. It is a gorgeous if tempermental stone.
Although it comes in a variety of colors including blue, greenish yellow, greenish blue, soft pink, and violet, I have seen it most often in varying shades of blue. You can see a range of blues - from peacock to London blue - from the photos here.
According to The Jeweler's directory of Gemstones, it's name is from the Greek word for "deceive" because it is often easily confused with other minerals like beryl, topaz, zircon, tourmaline, and sphene. Source countries include: Brazil, Canada, Mozambique, Madagascar, Mexico, Myanmar, Russia, Spain, Sri Lanka, and the US (California.) Typical inclusions are black carbon specks, cloudy inclusions, and fibrous inclusions (silk). It may be heat-treated to improve color and lessen inclusions.
A really lovely stone, it can be frustrating to work with because it is extremely brittle. I've had briolettes crack while I was stringing them because of pressure from adjacent stones. The corners also can chip relatively easily. At 5 Mohs, it is also fairly soft.
I've had better luck with more solid forms like teardrop briolettes and rondelles than with more delicate pear-shaped briolettes. In fact, because the necklace below needs delicate adjustment to be worn, I've kept it for myself. I love it, but I couldn't sell it because it does need to be handled in a particular way to make sure the briolettes don't crack.