Book List

Description: This rock is a granitoid containing feldspar phenocrysts. Phenocrysts are crystals that are significantly coarser-grained than the material surrounding it (aka: groundmass/matrix). This igneous texture is referred to as ‘porphyritic’. Porphyritic texture general forms when there is more than one distinct stage of magma cooling. For example, as the magma is cooling within a magma chamber (intrusive environment), minerals begin to grow and over time can grow to be quite large as the rate of cooling is slow and the magma remains liquid over vast periods of time. At some stage, the magma may be ejected from the magma chamber toward the surface of the Earth (extrusive environment), and the remaining unsolidified melt cools more rapidly resulting in finer-grained crystals or a glassy matrix.