There is a girlgroup with an AV (adult video, meaning p*rnstar) actress in it (named Anri) called Black Diamond.
Additionally, the jpop girlgroups Ebisu Muscats and BRW108 are entirely made of AV actresses.
There is also a kpop group called Honey Popcorn with Japanese AV actresses.
According to the book, The Tree of Qliphoth by The Temple of Ascending Flame, the black diamond is the philosopher's stone of the left hand path, and on page 10 it says,
"the Black Diamond, the emblem of perfection, individuality and Godhood. It is the Philosopher's Stone of the Left Hand Path, believed to be found in the depths of the Qliphoth, concealed and buried in the waste of creation. The quest for the Stone is also represented by the alchemical formula V.I.T.R.I.O.L., which means "Visit the interior of the earth, and by rectifying you will find the hidden stone." "
There is no further information about the black diamond in the book.
The book Tree of Qliphoth can be safely downloaded here, in pdf. Please click or touch the word "GET" to download the book.