rhamphotheca:

Malachite - Cu₂CO₃(OH)₂

… a copper carbonate hydroxide mineral. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures and spaces, deep underground, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare but do occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur. Typical malachite is laminated and whether or not microbes intervene in its formation is unknown…

(read more: Wikipedia)

(photos: Top/BL/BM -  Rob Lavinsky; BR -  JJ Harrison)