/fil'oh sil"i kit, -kayt'/, n.any silicate mineral having the tetrahedral silicate groups linked in sheets, each group containing four oxygen atoms, three of which are shared with other groups so that the ratio of silicon atoms to oxygen atoms is two to five.[1945-50; PHYLLO- + SILICATE]
* * *▪ mineralformerly called Disilicate,compound with a structure in which silicate tetrahedrons (a central silicon atom surrounded by four oxygen atoms at the corners of a tetrahedron) are arranged in sheets. Examples are talc and mica. Three of the oxygen atoms of each tetrahedron are shared with other tetrahedrons, but no two tetrahedrons have more than one oxygen atom in common; each tetrahedron, therefore, is linked to three others. The silicon atoms are arranged at the corners of hexagons, and the unshared oxygen atoms are commonly oriented on the same side of the sheet. Because these are capable of forming chemical bonds with other metal atoms, the silicate sheets are interleaved with layers of other elements. The various layers are stacked to form a grouping with the unshared oxygen atoms toward the centre, and these groups are weakly held together; this gives the phyllosilicates their distinct cleavage parallel to the layers. Phyllosilicates have chemical formulas that contain silicon (Si) and oxygen (O) in some multiple of Si2O5.
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