This is a ceramic aluminum oxide but it's commonly sold by scammers as lonsdaleite, which is a polymorph of diamond. I'm curious if anyone has inside info about how this got started. :
Star Seen Eating Planet For First Time - Videos from The Weather Channel
Vintage Stone Lonsdaleite Diamond 40.1 G and 3.40 Density - Etsy
Rare Lonsdaleite Diamond - Hexagonal Diamond - Original Tested - 150 Grams N | eBay