Mox Quartz

If Mox Quartz would enter the battlefield, you
may discard a colorless card instead. If you do,
put Mox Quartz onto the battlefield. If you
don't, put it into its owner's graveyard
{t}: Add {c} to your mana pool.
"Without life to react with it, the glistening oil will
eventually crystallize into something less dangerous,
even if only slightly." - Karn