It is distinctive in appearance, and while not a common igneous rock, does occur in this part of the state. To develop some skills in identifying igneous rocks. We see igneous rocks exposed on hill tops, in river valleys, and at the seashore. Igneous rocks also have considerable economic value. Igneous rocks are classified on the basis of texture and composition.
Texture is the overall size, shape and arrangement of mineral grains that make up the rock.
The size of the grains is very important. You will need a set of numbered igneous rock samples, a hand lens or magnifying glass, percentage estimation and identification charts, notebooks, pens, and possibly a small ruler. See definitions below. Plutonic rocks have cooled very slowly and have a coarse grained texture. Volcanic rocks have cooled quickly and show fine grained texture.