The creation of neotypes for hydrotalcite

Abstract Two samples of hydrotalcite, probably worked on by Carl Christian Hochstetter, have been discovered in the Museum für Naturkunde Berlin and given neotype status by the IMA CNMNC (proposal 15-J). The two samples from Snarum, Norway, have been reanalysed and give Mg 5.84 Al 2.07 Fe 0.09 (OH) 16 (CO 3 ) 1.08 ·4H 2 O and Mg 5.75 Al 2.21 Fe 0.04 (OH) 16 (CO 3 ) 1.12 ·4H 2 O. Both samples have a mix of the two polytypes 3 R /2 H in the ratio of 69.2/30.8 and 69.5/30.5%. A discussion of hydrotalcite and hydrotalcite-like phase occurrences in the literature is also presented.