Stilbite

Stilbite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named: * Stilbite-Ca * Stilbite-Na, sometimes also called stiblite Stilbite-Ca, by far the more common of the two, is a hydrous calcium sodium and aluminium silicate, NaCa 4 (Si 27 Al 9 )O 72 ·28(H 2 O). In the case of stilbite-Na, sodium dominates over calcium. The species are visually indistinguishable, and the series name stilbite is still used whenever testing has not been performed.

Stilbite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named: Stilbite-Ca Stilbite-Na, sometimes also called stiblite Stilbite-Ca, by far the more common of the two, is a hydrous calcium sodium and aluminium silicate, NaCa 4 (Si 27 Al 9 )O 72 ·28(H 2 O). In the case of stilbite-Na, sodium dominates over calcium. The species are visually indistinguishable, and the series name stilbite is still used whenever testing has not been performed. At one time heulandite and stilbite were considered to be identical minerals. After they were found to be two separate species, in 1818, the name desmine ("a bundle") was proposed for stilbite, and this name is still employed in Germany. The English name "stilbite" is from the Greek stilbein = to shine, because of the pearly luster of the {010} faces. Stilbite is usually monoclinic 2/m, meaning that it has one twofold axis of rotational symmetry perpendicular to a mirror plane. The twofold axis is the crystal axis b, and the a and c crystal axes lie in the mirror plane. For a monoclinic crystal a and c are inclined to each other at an angle β which is not a right angle. For stilbite β is nearly 130°. Stilbite crystals, however, appear to be almost orthorhombic, and a larger unit cell can be chosen, containing two formula units (Z = 2) such that resembles an orthorhombic cell, with all three crystal axes very nearly mutually perpendicular. The mineral is said to be pseudo-orthorhombic. Non-endmember forms of stilbite may be triclinic or even truly orthorhombic, indeed the framework can have symmetry ranging from orthorhombic to triclinic in a single crystal. Nx = 1.479 to 1.492, Ny = 1.485 to 1.500, Nz = 1.489 to 1.505 Nx = 1.484 to 1.500, Ny = 1.492 to 1.507, Nz = 1.494 to 1.513 == Unit cell and structure== Where sources give cell parameters for stilbite-Na, they are the same as those for stilbite-Ca. The unit cell can be considered as a monoclinic cell with β close to 130° and one formula unit per unit cell (Z = 1), or as a larger pseudo-orthorhombic cell with β close to 90° and Z = 2. Cell Parameters for the monoclinic cell: a = 13.595 to 13.69 Å, b = 18.197 to 18.31 Å, c = 11.265 to 11.30 Å, β = 127.94 to 128.1° a = 13.63 Å, b = 18.17 Å, c = 11.31 Å, β = 129.166° a = 13.60 to 13.69 Å, b = 18.20 to 18.31 Å, c = 11.27 Å, β = 128° Cell parameters for the pseudo-orthorhombic cell: a = 13.595 to 13.69 Å, b = 18.197 to 18.31 Å, c = 17.775 to 17.86 Å, β = 90.00 to 90.91° a = 13.595 to 13.657 Å, b = 18.197 to 18.309 Å, c = 17.775 to 17.842 Å, β = 90:05 to 90.91° (Z is doubled to Z = 4 because the formula unit halved to NaCa 2 Al 5 Si 13 O 36 .14H 2 O) a=13.69 Å, b=18.25 Å, c=11.31 Å, β =128.2° a = 13.60 to 13.69 Å, b = 18.20 to 18.31 Å, c = 17.78 to 17.86 Å, β = 90.0 to 90.91° The framework of stilbite is pseudo-orthorhombic with the open channels typical of zeolites. It has 10-member rings and 8-member rings forming channels parallel to a and pseudo-orthorhombic c respectively. ==Photo gallery== File:Stilbite-Ca-Celadonite-178645.jpg|Green Stilbite-Ca, which gets its color from inclusions of celadonite File:Fluorapophyllite-Stilbite-Ca-indi-71a.jpg|Clustered on a matrix of white chalcedony are a group of light salmon stilbite crystals; adjoining is a cluster of mint green fluorapophyllite crystals File:Stilbite-20450.jpg|Intergrown pinkish stilbite crystals showing the "bow-tie" tendency from Jalgaon District, Maharashtra, India. File:Stilbite Orange Fans.jpg|Stilbite crystal aggregates in fan shapes from Wassons Bluff, Nova Scotia. File:Stilbite-Ca-251147.jpg|Reddish-orange Stilbite-Ca from Jalgaon District, Maharashtra, India ==References== Attribution ==External links== Structure type STI

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