I am calling these black as I believe that is how most people will view the. If you hold them up to a very bright light you will see they are actually the darkest purple, but they don't really show that way. We have a number of styles of cabochons like this going up on the site. I wish I could tell you exactly what they are. It is my personal feeling that they are all glass. Now that is not what was supposedly sold to us. They came as  semi-precious stones  from a place "far-away".  Hmmm......well I suppose they could be some sort of dyed stone like howlite or some composite of some stone like substance. I really don't know,  anyway I am selling them as glass because that is my best guess.  They did not come labeled so even what they are "supposed" to be... I am unsure of.....if you know send us an e-mail.