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
Pressure cooking heat (less than high for induction cooking to allow air to be vented). Once the cooker reaches full pressure, the heat is lowered to maintain pressure; timing the recipe begins at this point. Recipes for foods using raising agents such as steamed puddings call for gentle pre-steaming, without pressure, in order to activate the raising agents prior to cooking and achieve a light, fluffy texture. It takes several minutes for the pressure cooker to reach the selected pressure level. It can take around 10 minutes or longer depending on: the quantity of food, the temperature of the food (cold or