Fukalite: An example of an OD structure with two-dimensional disorder

Abstract

The real crystal structure of fukalite, Ca 4 Si 2 O 6 (OH) 2 (CO 3 ), was solved by means of the application of order-disorder (OD) theory and was refined through synchrotron radiation diffraction data from a single crystal. The examined sample came from the Gumeshevsk skarn copper porphyry deposit in the Central Urals, Russia. The selected crystal displays diffraction patterns characterized by strong reflections, which pointed to an orthorhombic sub-structure (the "family structure" in the OD terminology), and additional weaker reflections that correspond to a monoclinic real structure.The refined cell parameters are a = 7.573 (3), b = 23.364 (5), c = 11.544(4) Å, β = 109.15(1)°, space group P2 1 /c. This unit cell corresponds to one of the six possible maximum degree of order (MDO) polytypes, as obtained by applying the OD procedure. The derivation of the six MDO polytypes is presented in the Appendix 1 . The intensity data were collected at the Elettra synchrotron facility (Trieste, Italy); the structure refinement converged to R = 0.0342 for 1848 reflections with I > 2σ(I) and 0.0352 for all 1958 data.The structure of fukalite may be described as formed by distinct structural modules: a calcium polyhedral framework, formed by tobermorite-type polyhedral layers alternating along b with tilleyitetype zigzag polyhedral layers; silicate chains with repeat every fifth tetrahedron, running along a and linked to the calcium polyhedral layers on opposite sides; and finally rows of CO 3 groups parallel to (100) and stacked along a.

Mosandrite: Structural and Crystal-Chemical Relationships With Rinkite

“…The tobermorite-like layer has been found not only in the various minerals of the tobermorite group, clinotobermorite (Merlino et al 2000), tobermorite 11 Å (Merlino et al 2001), tobermorite 14Å (Bonaccorsi et al 2005), and in the minerals of the rinkite group, as was first pointed out by Kadiyski et al (2008), but also in dovyrenite (Kadiyski et al 2008), in fukalite (Rastsvetaeva et al 2005;Merlino et al 2009) (Zanardi et al 2006).…”

Model structures for C-(A)-S-H(I)

“…The average value of the minimum distance decreases rather more rapidly than that of the average distance, whilst the average of the maximum distance is essentially constant, Merlino et al, 1999Merlino et al, , 2000; 11 Å tobermorite (normal; MDO 2 polytype; Merlino et al, 2001); 14 Å tobermorite (MDO 2 polytype; ; 9 Å clinotobermorite (MDO 2 polytype; Merlino et al, 1999Merlino et al, , 2000; afwillite (Malik & Jeffery, 1976); bultfonteinite (McIver, 1963;Biagioni et al, 2010); calcium chondrodite (Kuznetsova et al, 1980); chegemite (Galuskin et al, 2009); clinotobermorite (MDO 2 polytype; Merlino et al, 1999Merlino et al, , 2000; cuspidine (Saburi et al, 1977); dellaite (Safronov et al, 1981); fedorite (Mitchell & Burns, 2001); foshagite (Gard & Taylor, 1960); fukalite (Merlino et al, 2009); gyrolite (Merlino, 1988); hillebrandite (Dai & Post, 1995); jaffeite (Yamnova et al, 1993); jennite (Bonaccorsi et al, 2004); K-phase (Gard et al, 1981); kilchoanite (Taylor, 1971); killalaite (Taylor, 1977); nekoite (Alberti & Galli, 1980); okenite (Merlino, 1983); pectolite (Také uchi & Kudoh, 1977); poldervaartite (Dai et al, 1993); reyerite (Merlino, 1988); rosenhahnite (Wan et al, 1977); rustumite (Howie & Ilyukhin, 1977); scawtite (Zhang et al, 1992; cell parameter a given in the paper as 10.0394 is a mistake and has been corrected to 11.0394 Å ); suolunite (Ma et al, 1999); tilleyite (Grice, 2005); wollastonite 1 A (Ohashi, 1984); xonotlite <...>…”

OD approach to polytypism: examples, problems, indications

“…Actually there are only very few examples of OD structures built up by rods with ambiguity of rod stacking in two directions (DornbergerSchiff, 1964b;Merlino et al, 2009) and no systematic theory for such kind of OD structures has been so far developed. Possibly concepts and procedures to systematically deal with 'rod polytypism' will gradually emerge as far as the number of compounds displaying such kind of polytypism will substantially increase.…”