• journal_title：Clays and Clay Minerals
• Contributor：Cristina de la Calle ; Charles-Henri Pons ; Jacques Roux ; Vicente Rives
• Publisher：Clay Minerals Society
• Date：2003-
• Format：text/html
• Language：en
• Identifier：10.1346/CCMN.2003.0510201
• journal_abbrev：Clays and Clay Minerals
• issn：0009-8604
• volume：51
• issue：2
• firstpage：121
• section：Articles

A comparative crystallochemical study was performed on natural and synthetic hydrotalcite-like compounds with similar compositions. The nature of the brucite-like sheet stacking was addressed by means of powder X-ray diffraction. From the resulting electron diffraction patterns it was possible to establish the order-disorder of the cations in the brucite-like sheet. The results show that a natural sample from Snarum is an intergrowth of hydrotalcite (3R₁ polytype) and manasseite (2H₁ polytype) at a ratio of 77:23 (wt.%). An aluminian serpentine is associated with the hydrotalcite and manasseite minerals. The structure of a synthetic sample, Mg:Al = 2:1, was determined as space group R3̅m. For a few crystals in this sample, the octahedral cation distribution is compatible with the observed supercell (a = a′ √3). A second synthetic sample showed the presence of stacking faults and was described as a random layer sequence of two polytypes (3R and 2H).