Mcgovernite is a complex and interesting silicate as it is the species with the largest number of atoms in the unit cell. The formula for the species reads (Mn, Mg, Zn) 273As3+~12As5+~30Si~42O324(OH) 252. Mcgovernite is only found in one locality in the world according to Mindat http://www.mindat.org/min-2614.html
). The species was named after the famous Franklin mineral collector, J.J. McGovern. This specimen is a rich full cabinet sized piece featuring a thick zone of strong copper colored Mcgovernite on typical Franklin ore matrix. Simply one of the best examples of the species that I have seen, and certainly one of the largest display specimens of this unique material that I have handled in my life. Ex. Richard Kosnar Collection.