Porphyroblast

As porphyroblasts is referred to in mineralogy and petrology inclusions of larger crystals of a mineral species in a fine-grained matrix of other minerals. Porphyroblasts and matrix are referred to as Porphyroblastisches structure.

Porphyroblasts occur in metamorphic processes on both contact as well as in regionalmetamorphen rocks. The growth of the crystals is carried out in the solid state diffusion by rearrangement of the chemical constituents of the matrix. Consequently, they replace parts of the matrix. Porphyroblasts form where strong contrasts between the chemical and crystallographic properties of the matrix and porphyroblasts exist. This causes these crystals to grow faster than the slow-growing crystals of the matrix. Porphyroblasts vary in size from a few millimeters to several centimeters in diameter.

Common representatives porphyroblastischer training include andalusite, garnet, kyanite ( distension ), magnetite and staurolite. The matrix consists mostly of various carbonates, chlorites, feldspars, mica and quartz.