Not only do greenstones provide important geological clues regarding the history of the Earth, but they are also an economically important type of rock due to the valuable ores they often contain. Indeed, gold, silver, iron, copper, chromium, barium, nickel and a number of other metals may be found in belts of greenstone, where they are frequently heavily mined. Compact and hard, greenstones have occasionally been utilized as building stones as well. One of the most famous buildings constructed from the material is Bolingbroke Castle in Lincolnshire, England, which was established in the early thirteenth century and is particularly notable for being the birthplace of King Henry IV.