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Kentbrooksite is a moderately rare mineral of the eudialyte group, [2] with chemical formula (Na,REE) 15 (Ca,REE) 6 Mn 3 Zr 3 NbSi[(Si 9 O 27) 2 (Si 3 O 9) 2 O 2]F 2 ·2H 2 O. [3] This extended formula shows the presence of cyclic silicate groups and dominance of Si at the M4 site, according to the nomenclature of the eudialyte group. [4]
With two shared oxides bound to each silicon, cyclic or polymeric structures can result. The cyclic metasilicate ring Si 6 O 12− 18 is a hexamer of SiO 3 2-. Polymeric silicate anions of can exist also as long chains. In single-chain silicates, which are a type of inosilicate, tetrahedra link to form a chain by sharing two oxygen atoms each.
Zirsilite-(Ce) is a very rare mineral of the eudialyte group, with formula (Na, ) 12 (Ce,Na) 3 Ca 6 Mn 3 Zr 3 NbSi(Si 9 O 27) 2 (Si 3 O 9) 2 O(OH) 3 (CO 3)·H 2 O. [2] [3] The original formula was extended to show the presence of cyclic silicate groups and the presence of silicon at the M4 site, according to the nomenclature of the eudialyte group. [4]
Johnsenite-(Ce) is a very rare mineral of the eudialyte group, [2] with the chemical formula Na 12 (Ce,La,Sr,Ca,[ ]) 3 Ca 6 Mn 3 Zr 3 WSi(Si 9 O 27) 2 (Si 3 O 9) 2 (CO 3)O(OH,Cl) 2. [3] The original formula was extended to show the presence of both the cyclic silicate groups and silicon at the M4 site, according to the nomenclature of the eudialyte group. [4]
Cyclic compounds that have both carbon and non-carbon atoms present are heterocyclic carbon compounds, and the name refers to inorganic cyclic compounds as well (e.g., siloxanes, which contain only silicon and oxygen in the rings, and borazines, which contain only boron and nitrogen in the rings). [5]
Regular coordination is not always present: for example, it is not found in Ca 2 SiO 4, which mixes six- and eight-coordinate sites for Ca II. Soro-silicates, involving discrete double or triple tetrahedral units, are quite rare: metasilicates involving cyclic [(SiO n 3)] 2n− units of corner-abutting tetrahedra forming a polygonal ring are ...
Reverse weathering is often found in river deltas as these systems have high sediment accumulation rates and are observed to undergo rapid diagenesis. [18] The formation of silicate clays removes reactive silica from the pore waters of sediment, increasing the concentration of silica found in the rocks that form in these locations. [18]
Group 1 silicides are in general high melting, metallic grey, with moderate to poor electrical conductance and prepared by heating the elements. Superconducting properties have been reported for Ba 8 Si 46. [6] Several silicon Zintl ions (Si 4− 4, Si 4− 9, Si 2− 5) are known with group 1 counterions. [7]