Poudretteite is named after the Poudrette family, operators of the quarry where the mineral was discovered. Poudrettite forms transparent violet to pink roughly equant barrel-shaped prismatic crystals. Poudretteite is a very rare material. Clean gems over 1 ct are uncommon.
Benitoite is a rare gemstone, and for all practical purposes only comes from a single limited deposit in California. It is a relatively new gemstone, and was first discovered in 1907. Benitoite gemstones have a sapphire-blue color, and can have very good transparency and luster.
In mineralogy, the name Musgravite refers to the mineral called Magnesiotaaffeite-6N’3S. It crystallizes in the trigonal system. The closely-related Magnesiotaaffeite, which crystallizes in the hexagonal system, is known in mineralogy as Magnesiotaaffeite-2N’2S.
Since grandidierite is quite hard, high quality material has been cut as gemstones, making it one of the very rarest gems, in a class with varieties like benitoite, painite, taaffeite and jeremejevite. You will often see grandidierite included in lists of the 10 rarest gem varieties in the world.