TY - JOUR

T1 - Crystal chemistry of natural layered double hydroxides

T2 - 4. crystal structures and evolution of structural complexity of quintinite polytypes from the kovdor alkaline-ultrabasic massif, kola peninsula, Russia

AU - Zhitova, Elena S.

AU - Krivovichev, Sergey V.

AU - Yakovenchuk, Viktor N.

AU - Ivanyuk, Gregory Yu

AU - Pakhomovsky, Yakov A.

AU - Mikhailova, Julia A.

PY - 2018/4/1

Y1 - 2018/4/1

N2 - Two quintinite polytypes, 3R and 2T, which are new for the Kovdor alkaline-ultrabasic complex, have been structurally characterized. The crystal structure of quintinite-2T was solved by direct methods and refined to R1 = 0.048 on the basis of 330 unique reflections. The structure is trigonal, Pc1, a = 5.2720(6), c = 15.113(3) Å and V = 363.76(8) Å 3 . The crystal structure consists of [Mg2Al(OH)6] + brucite-type layers with an ordered distribution of Mg 2+ and Al 3+ cations according to the × superstructure with the layers stacked according to a hexagonal type. The complete layer stacking sequence can be described as ... =Ab1C = Cb1A=.... The crystal structure of quintinite-3R was solved by direct methods and refined to R1 = 0.022 on the basis of 140 unique reflections. It is trigonal, Rm, a = 3.063(1), c = 22.674(9) Å and V = 184.2(1) Å 3 . The crystal structure is based upon double hydroxide layers [M 2+,3+ (OH)2] with disordered distribution of Mg, Al and Fe and with the layers stacked according to a rhombohedral type. The stacking sequence of layers can be expressed as ... =D?B = BC = CA=... The study of morphologically different quintinite generations grown on one another detected the following natural sequence of polytype formation: 2H → 2T → 1M that can be attributed to a decrease of temperature during crystallization. According to the information-based approach to structural complexity, this sequence corresponds to the increasing structural information per atom (IG): 1.522 → 1.706 → 2.440 bits, respectively. As the IG value contributes negatively to the configurational entropy of crystalline solids, the evolution of polytypic modifications during crystallization corresponds to the decreasing configurational entropy. This is in agreement with the general principle that decreasing temperature corresponds to the appearance of more complex structures.

AB - Two quintinite polytypes, 3R and 2T, which are new for the Kovdor alkaline-ultrabasic complex, have been structurally characterized. The crystal structure of quintinite-2T was solved by direct methods and refined to R1 = 0.048 on the basis of 330 unique reflections. The structure is trigonal, Pc1, a = 5.2720(6), c = 15.113(3) Å and V = 363.76(8) Å 3 . The crystal structure consists of [Mg2Al(OH)6] + brucite-type layers with an ordered distribution of Mg 2+ and Al 3+ cations according to the × superstructure with the layers stacked according to a hexagonal type. The complete layer stacking sequence can be described as ... =Ab1C = Cb1A=.... The crystal structure of quintinite-3R was solved by direct methods and refined to R1 = 0.022 on the basis of 140 unique reflections. It is trigonal, Rm, a = 3.063(1), c = 22.674(9) Å and V = 184.2(1) Å 3 . The crystal structure is based upon double hydroxide layers [M 2+,3+ (OH)2] with disordered distribution of Mg, Al and Fe and with the layers stacked according to a rhombohedral type. The stacking sequence of layers can be expressed as ... =D?B = BC = CA=... The study of morphologically different quintinite generations grown on one another detected the following natural sequence of polytype formation: 2H → 2T → 1M that can be attributed to a decrease of temperature during crystallization. According to the information-based approach to structural complexity, this sequence corresponds to the increasing structural information per atom (IG): 1.522 → 1.706 → 2.440 bits, respectively. As the IG value contributes negatively to the configurational entropy of crystalline solids, the evolution of polytypic modifications during crystallization corresponds to the decreasing configurational entropy. This is in agreement with the general principle that decreasing temperature corresponds to the appearance of more complex structures.

KW - Hydrotalcite supergroup

KW - Kovdor phoscorite-carbonatite complex

KW - Natural layered double hydroxides

KW - Quintinite

UR - http://www.scopus.com/inward/record.url?scp=85049929066&partnerID=8YFLogxK

U2 - 10.1180/minmag.2017.081.046

DO - 10.1180/minmag.2017.081.046

M3 - Article

AN - SCOPUS:85049929066

VL - 82

SP - 329

EP - 346

JO - Mineralogical Magazine

JF - Mineralogical Magazine

SN - 0026-461X

IS - 2

ER -