Aminoffite, named in honor of Dr. G. Aminoff, is found at Längban in veins cutting magnetite and limonite. It is tetragonal; a : c = 1 :: 0.7116. The crystals are clear and colorless with {111} and {001} the only forms. Imperfect (001) cleavage is present. H = 5.5. G = 2.94. Uniaxial negative ω = 1.647, ε = 1.637. Dimensions of the unit cell: a0= 13.8 Å, c0= 9.8 Å, Space group: 14/mmm. Chemical analysis and unit cell determitation yield the composition