The answer is:
-when Jackhammer is a huge hammer used to breaking up the hard rocks and the hard materials to smaller pieces.
-and the metamorphic rocks are type of rocks which change to metamorphic rock by heating and high pressure so, the chemical and physical properties of the rock will be changed.
-and here in cause of using the Jackhammer there is no change in the chemical or physical properties of the original rock and no high temp(more than 200°C ) or high pressure to change to metamorphic rock . It is just a breaking up of the rock to small parts.