Sparkly Gems

Riddle: If you like pretty gems that sparkle and shine,
I invite you to dig in my virtual mine.
My first is purple, fit for a king,
My second is green where Dorothy did her thing.
My third is red, July's birthstone as well,
My fourth is seen in strings and is found inside a shell.
My fifth is hard, pure Carbon and expensive to buy,
My sixth is Crocodolite, striped like the big cat's eye.
Seventh is two words, a man-made fake of April's stone,
Eighth is very dark and found at Lightning Ridge alone.
Now take from each gem, one letter in its turn,
And you will find the stuff for which even the god's yearn.