Purple Fluorite Shard is a common Gemstone, primarily of use for bartering, or sale to Traders.
A common Underdark crystal, fluorite seems to form anywhere where light is scarce, though only bigger stones are suitable for mining.
Properties
Miscellaneous Items
Rarity: Common
Weight: 0.05 kg / 0.1 lb
Price: 5 gp 
UID
LOOT_Alchemy_Crystal_PurpleFluoriteShard
Where to find
They can be collected by destroying Glowing Gems in The Underdark.
Notes
Even though it is defined in the game files as an Alchemy Crystal, unlike similar crystals, this variant has no current known use in Alchemy.