I don't know if this would make much sense, but it's NOT in the periodic table so HA!
I still want something incredibly strong to satisfy my destructive needs, how about Sapphire? It's the 2nd hardest gem after diamond, and in The Powder Toy, it would basically be the finite version of diamond, except it melts under EXTREMELY high temperature (way past 3500, up to 8000/9000), and can resist pressure up to 90/100 (I still don't know what to call pressure in TPT, at least in terms of numbers).
The name doesn't matter much, just that it's awesome. If you do happen to choose Sapphire as the name, it could glow a pretty blue color :D other than that, it doesn't conduct. If we want to be less 'realistic' you could name is Zircon which is basically fake diamond? Or Quartz, whatever. Breaks into broken glass.
its a bad idea from a dev side because people expect huge chemical reactions and "because elementX has been added, why not elementY which works with elementX to make elementZ"
The best example is you wanting O2 to be made when H2O2 and WATR mix...