Research Article| December 01, 2016
The crystal chemistry of lamprophyllite-related minerals: a review
Ramiza K. Rastsvetaeva;
Ramiza K. Rastsvetaeva *
Shubnikov Institute of Crystallography RAS, Moscow, 119333, Russia
Corresponding author e-mail: rast@ns.crys.ras.ru
Nikita V. Chukanov;
Nikita V. Chukanov
Institute of Problems of Chemical Physics, Chernogolovka, Moscow region, 142432, Russia
Sergey M. Aksenov
St. Petersburg State University, St. Petersburg, 199034, Russia
Ramiza K. Rastsvetaeva, Nikita V. Chukanov, Sergey M. Aksenov; The crystal chemistry of lamprophyllite-related minerals: a review. European Journal of Mineralogy ; 28 (5): 915–930. doi: https://doi.org/10.1127/ejm/2016/0028-2560
The crystal structures of the lamprophyllite-related minerals are based upon HOH modules consisting of a central octahedral O sheet sandwiched between two heteropolyhedral H sheets. The general crystal-chemical formula for these minerals can be written as [10–11]A2 [[6]M1[6]M22[6]2M3X2] [[5]L2(Si2O7)2O2], where the contents of the O and H sheets are given in square brackets in this order and A = Ba, Sr, K, Na,; M1 = Na, Mn2+; M2 = Na, Mn2+, Fe2+, Ca; M3 = Ti, Mn2+, Mg, Fe3+, Fe2+; L = Ti, Fe3+; X = OH, O, F. According to the unit-cell parameters and symmetry, lamprophyllite-related minerals can be subdivided into five structure types: I (monoclinic polytypes, C2/m); II (orthorhombic polytypes, Pnmn), III (nabalamprophyllite, BaNa[Na3Ti (OH)2][Ti2(Si2O7)2O2], monoclinic, P2/m, with an ordered arrangement of the interlayer Ba2+ and Na+ cations), IV (triclinic, P1) and V (triclinic, P1¯⁠). The triclinic members (types IV and V) include schüllerite and its analogues, which differ from the lamprophyllite-group minerals sensu stricto in their symmetry and topology of the HOH modules. The end-member formulae of lamprophyllite-related minerals and the position of schüllerite in the ranks of heterophyllosilicates are discussed.
crystal chemistry
crystal systems
monoclinic system
order-disorder
orthorhombic system
polytypism
triclinic system
lamprophyllite
barytolamprophyllite
nabalamprophyllite
schullerite
lamprophyllite group
fluorlamprophyllite