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
Slate (magazine) working on a long, ambitious project of some sort," Plotz said in an interview. "Slate" introduced a paywall-based business model in 1998 that attracted up 20,000 subscribers but was later abandoned. A similar subscription model was implemented in April 2001 by "Slate"s independently owned competitor, Salon.com. "Slate" started a daily feature ”Today's Pictures” on November 30, 2005, which featured 15-20 photographs from the archive at Magnum Photos that share a common theme. The column also features two flash animated ”Interactive Essays” a month. "Slate" was nominated for four digital National Magazine Awards in 2011 and won the NMA for General