SILICATE

Fillers in plastics and rubber, paper coatings, antacids, anticaking agents, cements.

silicate: Any of a group of substancescontaining negative ionscomposed of silicon and oxygen. Thesilicates are a very extensive groupand natural silicates form the majorcomponent of most rocks (see silicateminerals). The basic structural unit is the tetrahedral SiO4 group. This may occur as a simple discrete SiO₄^4– anion as in the orthosilicates, e.g. phenacite (Be₂SiO₄) and willemite (Zn₂SiO₄). Many larger silicate species are also found (see illustration). These are composed of SiO4 tetrahedra linked by sharing oxygen atoms as in the pyrosilicates, Si₂O₇^6–, e.g. Sc₂Si₂O₇. The linking can extend to such forms as bentonite, BaTiSi₃O₉, or alternatively inÜnite chain anions, which are single strand (pyroxenes) or double strand (amphiboles). Spodumene, LiAl(SiO₃)₂, is a pyroxene and the asbestos minerals are amphiboles. Large two-dimensional sheets are also possible, as in the various micas (see illustration), and the linking can extend to full threedimensional framework structures, often with substituted trivalent atoms in the lattice. The zeolites are examples of this.

Any of the widely occurring compounds containing silicon, oxygen, and one or more metals with or without hydrogen. The silicon and oxygen may combine with organic groups to form silicate esters. Most rocks (except limestone and dolomite) and many mineral

(Natural silicate dusts) Toxic by inhalation.

Any of the widely occurring compounds containing silicon, oxygen and one or more metals with or without hydrogen is called silicate. The silicon and oxygen may combine with organic groups to form similar esters. Most rocks and many minerals, except limestone and dolomite, are silicates. Typical natural silicates are gemstones, except for diamond. Portland cement, because it is manufactured from chalk and clay, contains a high percentage of calcium silicates.
Sodium silicate is the best known of the synthetic silicates.