Lamprophyllite
| Lamprophyllite | |
|---|---|
| File:Lamprophyllite Basic sodium strontium barium titanium fluo-silicate Kola Peninsula, Russia 2882.jpg | |
| General | |
| Category | Silicate mineral |
| IMA symbol | Lmp[1] |
Lamprophyllite (named for its lustrous cleavage) is a rare, but widespread mineral Ti-silicate mineral usually found in intrusive agpaitic igneous rocks. Yellow, reddish brown, Vitreous, Pearly.[2]
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.[3]
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.[4]
Lamprophyllite is monoclinic, The mineral also has an orthorhombic polytype[5] Unit-cell parameters mainly depend from the cationic composition in the interlayer position A[6] 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.[7]
Lamprophyllite melts incongruently (880 °C) with formation of titanium oxides: rutile, tausonite, freudenbergite. Synthetic lamprophyllite synthesis was crystallized from melt. Newly formed lamprophyllite show higher Sr/Ba ratio than in equilibrium melt.[8]
References
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