Metamorphic rock 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 texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath
Well-formed element Type Definition). Well-formed element In web page design, and generally for all markup languages such as SGML, HTML, and XML, a well-formed element is one that is either a) opened and subsequently closed, or b) an empty element, which in that case must be terminated; and in either case which is properly nested so that it does not overlap with other elements. For example, in HTML: codice_1 is a well-formed element, while codice_1 is not, since the bold element is not closed. In XHTML, and XML, empty elements (elements that inherently have no content) are terminated by putting a slash