What is the rarest rock type on earth

Martian rocks are very rare, but if you are asking which rock type that forms on Earth then the answer would be a komatiite. It is an igneous rock that is a fine grained (volcanic) equivalent of a peridotite (which are also fairly rare). But you could get more specific and say that a kimberlite with diamonds in it is pretty rare or a conglomerate with platinum nuggets or a entire list of rare minerals in rocks, but, of all of the normal rock types out there, the komatiite is very rare.

Here is a link to this very rare rock type: http://en.wikipedia.org/wiki/Komatiite

i googled it but its sketchy but one answer said martian rocks...