That would not impact a mastodon tusk - that would preferate the mastodon tusk.
Actually, anything large enough to strike at 6,214 miles per second, and yet reach the ground without burning up in the atmosphere, would not merely "impact" OR "perforate" a mammoth tusk. I tend to think it would vaporize the tusk, plus the other tusk, plus the rest of the mammoth, plus the whole remaining herd of mammoths, plus everything else including solid rock for a hemispherical radius of hundreds or thousands of feet.
-ccm
and not just the tusk, but the whole elephant, and everything else around. 6K miles per second is moving.