Lamprophyllite

Lamprophyllite (named for its lustrous cleavage) is a rare, but widespread mineral Ti-silicate mineral usually found in intrusive agpasitic igneous rocks. Yellow, reddish brown, Vitreous, Pearly.[1]

Lamprophyllite
General
CategorySilicate mineral

Lamprophyllite formula is (Sr,Ba,K,Na)2Na(Na,Fe,Mn)2Ti[Ti2O2(Si2O7)2[(O, OH,F)2 . Full isomorphic range between lampropyllite and baritollalpropyllite exist.[2]

The general crystal-chemical formula for lampropyllite-related minerals can be written as A2[(M1)(M2)2(M3)X2] [[5] L2(Si2O7)2O2], where the contents of the O and H sheets are given in square brackets in this order and A = Sr, Ba,K, Na; M1 = Na, Mn2+; M2 = Na, Mn2+, Fe2+, Ca; M3 = Ti, Mn2+, Mg, Fe3+, Fe2+; L = Ti, Fe3+; X = OH, O, F.[3]

Lamprophyllite is monoclinic, The mineral also has an orthorhombic polytype[4] Unit-cell parameters mainly depend from the cationic composition in the interlayer position A[5] 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.[6]

Lamprophyllite melts incongruently (880 °C) with formation of titanium oxides: rutile, tausonite, freudenbergite. Syntetic lamprophyllite synthesis was crystallized from melt. Tewly formed lamprophyllite show higher Sr/Ba ratioi than in equilibrium melt.[7]

Pseudobinare phase diagram lamprophyllite-nepheline


References
  1. https://www.mindat.org/min-2315.html
  2. Zaitsev V.A. Kogarko L.N. (2002). "Compositions of Minerals of the Lamprophyllite Group from Alkaline Massifs Worldwide". Geochemistry International. 40: 313–322.
  3. Rastsvetaeva, Ramiza K.; Chukanov, Nikita V.; Aksenov, Sergey M. (2016-12-31). "The crystal chemistry of lamprophyllite-related minerals: a review". European Journal of Mineralogy. 28 (5): 915–930. doi:10.1127/ejm/2016/0028-2560.
  4. Krivovichev, Sergey V.; Armbruster, Thomas; Yakovenchuk, Viktor N.; Pakhomovsky, Yakov A.; Men'shikov, Yuriy P. (2003-08-01). "Crystal structures of lamprophyllite-2M and lamprophyllite-2O from the Lovozero alkaline massif, Kola peninsula, Russia". European Journal of Mineralogy. 15 (4): 711–718. doi:10.1127/0935-1221/2003/0015-0711. ISSN 0935-1221.
  5. Zaitsev, V. A. (May 2005). "Numerical dependence of the unit-cell parameters of minerals of the lamprophyllite group on the cationic composition in the interlayer position". Crystallography Reports. 50 (3): 379–381. doi:10.1134/1.1927593. ISSN 1063-7745.
  6. Rastsvetaeva, Ramiza K.; Chukanov, Nikita V.; Aksenov, Sergey M. (2016-12-31). "The crystal chemistry of lamprophyllite-related minerals: a review". European Journal of Mineralogy. 28 (5): 915–930. doi:10.1127/ejm/2016/0028-2560.
  7. VA Zaitsev, LD Krigman, LN Kogarko (2004). "Pseudobinare phase diagram lamprophyllite-nepheline". Lithos. EMPG-X special volume.CS1 maint: multiple names: authors list (link)
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