50 State Quarters to form what is known as a "mule". Only sixteen of these specimens, produced on dollar planchets, escaped from the mint. A 2005 Minnesota double die quarter, as well as a 2005 Minnesota quarter with extra trees (another die error), have both triggered numismatic interest. An unusual die break on some 2005 Kansas quarters created a humpback bison. Relatively more common are Kansas quarters bearing the motto "IN GOD WE RUST." The United States produces proof coinage in circulating base metal and, since 1992, in separately sold sets with the dimes, quarters, and half-dollars in silver. For the silver issues,
Major thirds tuning also facilitate advanced guitarists' improvisation, precisely the aim of jazz guitarist Ralph Patt when he began popularizing major-thirds tuning between 1963 and 1964. In standard tuning, the successive open-strings mix two types of intervals, four perfect-fourths and the major third between the G and B strings: Only major thirds occur as open-string intervals for major-thirds tuning, which is also called ""major-third" tuning", ""all-thirds" tuning", and ""M3" tuning". A popular M3 tuning has the open strings in which the low G is a major third above the low E of standard tuning. Consequently, a seventh string for the low E is