№ 3,
2016
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Crystalochemical peculiarities of laumontite in Eocene volcanogenic strata of Talysh (Azerbaijan)
Baku State University, AZ1148, Baku, Z. Khalilov str., 23, E-mail: afashf@rambler.ru
Summary
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To clarify the structure of laumontite parameters of the unit cell (a=14,7162(9)Ǻ, b=13,0676(8) Ǻ, c=7,5711(5) Ǻ, β=111,8550(10)0, sp. gr. C2) were identified and obtained a full diffractometer APEX – II (MoKα-radiation). According to the results of PSA crystal chemical formula of the mineral (Ca0.9Na0.1)(H2O)3(Al0.9Si0.1)(AlSi4O12)0,675H2O (z=4) was determined. It was found that in the structure of laumontite (SiO4) tetrahedra form a four membered rings – Si4O12 which contacting with AlO4-tetrahedra, form grids with four and twelve-voids. Nets, knitted two-fold axis, create a frame with the composition (Al8Si16O48), whear (Si-O)m.= 1,615Å, (Al-O)m.=1,736Å; (O-Si-O)m.=109,470, (Si-O-Si)m.=139,20, (O-Al-O)m.=109,50; (Si-O-Al)m.=136,70.
In the frame cavities calsium atom is coordinated by four bridging oxygen ((Ca,Na)-O)ср.=2,448Å and three water molecules ((Ca,Na)-H2O)ср.=2,391Å, that form around a single-cap calcio trigonal prism. Coordinating and free water molecules contacting with the hydrogen bond form clathrate as bicapped trigonal prism.
Structural similarity of laumontite, wairacyte, analcime and pollucite was identified and binding properties of Ca-zeolites were crystallochemically found.