Q:

How do I breed a Malachite dragon? 

I have heard reports of the Malachite dragon not being in the shop but being a possible new dragon introduced with the Pollen Dragon. 
Is this a gem dragon? ( isn't malachite technically a mineral??) 

A:

You need to breed a plant dragon with a metal hybrid as the Wiki says.  Apparently it is important that the metal dragon is the hybrid one, as there are several similar pairings between incompatible dragons where choosing which dragon is the hybrid determines which breeding result you can get. 
Note you can't directly breed a plant and metal dragon; alone they are incompatible.