A temperature-induced reversible transformation between paratacamite and herbertsmithite

Structural complexity and crystallization: the Ostwald sequence of phases in the Cu2(OH)3Cl system (botallackite–atacamite–clinoatacamite)

“…4. The condensation of chains by sharing common Cu corners leaves one of the Cu atoms not bonded to Cl, and this is the position that is substituted by Zn, Mg and Ni in other atacamite group minerals [44][45][46][47][48][49].…”

Structural and compositional variations of basic Cu(II) chlorides in the herbertsmithite and gillardite structure field

“…The associated solid-solution series is apparently continuous and extends to the minerals herbertsmithite, Cu 3 Zn(OH) 6 Cl 2 (Braithwaite et al, 2004), gillardite, Cu 3 Ni(OH) 6 Cl 2 (Colchester et al, 2007;Clissold et al, 2007), leverettite, Cu 3 Co(OH) 6 Cl 2 (Kampf et al, 2013b) and tondiite, Cu 3 Mg(OH) 6 Cl 2 (Malcherek et al, 2014) (isostructural, trigonal, space group R3 m), depending upon the nature of the dominant substituting cation. This R3 m structure corresponds to a pronounced substructure inherent in paratacamite (Fleet, 1975;Kampf et al, 2013a;Sciberras et al, 2013;Welch et al, 2014) and may be considered as the aristotype model for the group of basic Cu(II) chlorides (Malcherek and Schlüter, 2009). This group has received much attention in recent years due to their structure induced magnetic properties, as they are so-called "frustrated antiferromagnets" (Schores et al, 2005;Helton et al, 2007;Freedman et al, 2010;Chu et al, 2010;Han et al, 2011Han et al, , 2012Li and Zhang, 2013).…”

“…Malcherek and Schlüter (2009) suggested that the sequence of compositionally related structural transformations that lead to herbertsmithite can be described by the space group chain P1 → P2 1 /c (P2 1 /n) →R3 m. However, the triclinic phase originally attributed to the series, known as "anatacamite", has recently been discredited by the Commission on New Minerals Nomenclature and Classification of the International Mineralogical Association (Hålenius et al, 2015). Welch et al (2014) reported a reversible structural transformation from paratacamite R3 to herbertsmithite R3 m structures that occurs at 353-393 K. This transformation is in line with the predicted space group chain associated with the paratacamite phase, P1 → R3 → R3 m (Malcherek and Schlüter, 2009). The boundary between the R3 and R3 m phases is difficult to quantify due to the very similar powder X-ray diffraction patterns of the minerals (Jambor et al, 1996;Braithwaite et al, 2004;Kampf et al, 2013a;Sciberras et al, 2013).…”

“…The boundary between the R3 and R3 m phases is difficult to quantify due to the very similar powder X-ray diffraction patterns of the minerals (Jambor et al, 1996;Braithwaite et al, 2004;Kampf et al, 2013a;Sciberras et al, 2013). The superstructure reflections of paratacamite may only be quantifiable using single-crystal diffraction methods (Kampf et al, 2013a;Sciberras et al, 2013;Welch et al, 2014). Braithwaite et al (2004) suggested an upper compositional limit for the stability of paratacamite of ca 50% interlayer occupancy of Zn, which implies a destabilisation of the herbertsmithite structure below this threshold.…”

“…Braithwaite et al (2004) suggested an upper compositional limit for the stability of paratacamite of ca 50% interlayer occupancy of Zn, which implies a destabilisation of the herbertsmithite structure below this threshold. Paratacamite from the type material (British Museum specimen BM86958) was reported by Welch et al (2014) as having the composition Cu 3.71 Zn 0.29 (OH) 6 Cl 2 , which is in line with the observations made by Braithwaite et al (2004) and Jambor et al (1996). However, recent reports of paratacamite-(Mg) (Kampf et al, 2013a) and paratacamite-(Ni) (Sciberras et al, 2013) both with a composition significantly greater than 50% occupancy of the interlayer by the substituting cation has indicated that the compositional stability fields of paratacamite and herbertsmithite congeners may be significantly different from those of these two minerals.…”