Metamorphic rocks arise from the transformation of existing rock types due to extreme heat and pressure. This process is called metamorphism, which means change in form. The set includes anthracite, biotite schist, gneiss, marble black, marble green, marble pink, marble white, mica schist, phyllite, quartzite gray, quartzite green, quartzite white, serpentine, slate, tiger eye. Average sizes are 2 cm X 3 cm X 1.5 cm