Zircon?

Nothing Says "Early Earth Was Cool" Like World's Oldest Diamonds
The zircon in imitation diamonds proves the best way to preserve more than four-billion-year-old versions of the real thing
By David Biello
Source:
http://www.sciam.com/article.cfm?articleID=8F37399C-E7F2-99DF-30361B86A598909B&chanID=sa007