Friedrich Mohs harder. This became the basis of the hardness scale developed by Mohs. The hardest mineral, diamond was given a value of 10 and softer minerals such as talc were given the very low value of 1 (unity). Other minerals were given intermediate values, depending on their ability to scratch another mineral in the scale. Thus gypsum was given the value 2 because it will scratch talc crystals, and calcite the value 3 because it will scratch gypsum. Minerals are also now classified by chemical characteristics, but the physical properties are still useful in field examination. In 1812, Mohs became a
Ikranite Ikranite Ikranite is a member of the eudialyte group, named after the Shubinov Institute of Crystallography of the Russian Academy of Sciences. It is a cyclosilicate mineral that shows trigonal symmetry with the space group "R"3"m", and is often seen with a pseudo-hexagonal habit. Ikranite appears as translucent and ranges in color from yellow to a brownish yellow. This mineral ranks a 5 on Mohs Scale of Hardness, though it is considered brittle, exhibiting conchoidal fracture when broken. The eudialyte group currently consists of 27 known minerals (see below), all considered rare, with the exception of eudialyte. The list below