Metamorphic rock the foliation is called "gneissosity"), granoblastic (includes granulite, some marbles and quartzite), and hornfelsic (includes hornfels and skarn). Metamorphic rock Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure ( or more), causing profound physical or chemical change. The protolith may be a sedimentary, igneous, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by
Heat press technology in newer machines enables precise control of heat and pressure levels and timing. The most common types of heat press employ a flat platen to apply heat and pressure to the substrate. In the "clamshell" design, the upper heat element in the press opens like a clamshell, while in the "swing-away" design, the heat platen swings away from the lower platen. Another design type a "draw style press" allows for the bottom platen to be pulled out like a drawer away from the heat for preparation of the graphic. Vacuum presses utilize air pressure to provide the necessary force