| Lamprophyllite | |
| Category: | Silicate mineral |
| Imasymbol: | Lmp[1] |
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.[2]
Lamprophyllite formula is (Sr,Ba,K,Na)2Na(Na,Fe,Mn)2Ti[Ti<sub>2</sub>O<sub>2</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>[(O, OH,F)<sub>2</sub> . Full isomorphic range between lampropyllite and baritollalpropyllite exist.<ref>{{Cite journal|last=Zaitsev V.A. Kogarko L.N.|date=2002|title=Compositions of Minerals of the Lamprophyllite Group from Alkaline Massifs Worldwide|journal=Geochemistry International|volume=40|pages=313–322}}</ref> 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]