geology

Those classified as plagioclase are triclinic and include andesine and anorthite, while barium ones
are monoclinic and include celsian and hyalophane. Another classification, alkali, applies to those such
as orthoclase and microcline that fall between the (*) potassium variety and albite. These rocks have a
name from the German for field rock or rock without ore, and their crystals can sometimes be found in
granite. For 10 points, the orthoclase type of what group of minerals, the most abundant group found in the
earth’s crust, has a Mohs hardness of six?