Is this a chemical or physical change

Good question.  if it's a physical change what you would see is a change in the physical object/appearance like let's say I Tear a piece of paper, that would be a Physical change.  I believe your answer would be a chemical change.  

answer and explanation;

composition refers to both the types of minerals within a rock and the overall chemical makeup of the rock while texture refers to the size and arrangement of the minerals or grains that make up a rock. both composition and texture can be used to classify rocks, such as igneous rocks. texture describes how the rock became solid or crystallized from liquid, melted rock. composition of a rock describes the minerals that make up a particular rock.