Silicate, chemical formula Structure

Silicates also exist in which each silicon atom bonds to one outer oxygen and to three inner oxygen atoms. The result is a linked network in which every silicon atom forms three Si—O—Si links, giving a planar, sheet-like structure. The empirical formula of this silicate is S12 O5. In many minerals, aluminum atoms replace some of the silicon atoms to give aluminosilicates. The micas—one has the chemical formula... 

In the silicate crystal chemistry, compounds such as Mg3Al2Si30i2 are classified within the orthosilicates owing to the isolated Si044+ tetrahedra existing in their structure, and better described by a chemical formula such as Mg3Al2(Si04)3. 

Quartz is the most common mineral in the Earth s crust. It occurs in a wide variety of forms, colors, and lusters, but other properties are generally consistent for all specimens. All quartz has the same basic chemical formula, silicon dioxide (SiC ). It has a hardness of 7, and a distinctive conchoidal fracture. The color and translucency of quartz can be affected by a disruption of the molecular structure, as in smoky quartz, or by the inclusions of tiny amounts of other elements or minerals. In some classifications, quartz is listed with the oxides, but it is most often placed with the silicates. 

Chemical formulae in cement chemistry are often expressed as a sum of oxides thus tricalcium silicate, CajSiO, can be written as 3Ca0 Si02- This does not imply that the constituent oxides have any separate existence within the structure. It is usual to abbreviate the formulae of the commoner oxides to single letters, such as C for CaO or S for SiOj, CajSiOj thus becoming CjS. This system is often combined with orthodox chemical notation within a chemical equation, e.g. 

Kaolinite. The composition of this mineral is close to the empiric formula Al20j-2Si02-2H20 while structural chemical formula of aluminium silicate is Al2(Si205](OH)4. It has triclinic syngony, PI space group, unit cell parameters are a = 0.515, b = 0.895, c = 0.737 nm, a = 9i°48, 3 = 104°30, y = 90°(z = 2). 

Armbruster [14]. The structure of 14A-Tobermorite (equivalent to the CSH cement phase) is usually inferred from that of 11 A-Tobermorite and its ideal chemical formula is Ca22XSifi., pH %H20. The primary structural unit of Tobermorite contains CaO polyhedral sheets sandwiched between single silicate chains. The silicate chains are based on a three units repeating pattern called dreierketten arrangement of 7.8A in length in which two of the tetrahedra point toward the CaO polyhedral sheet while the third points toward the interlayer void. 

Using Table 22.1, predict the kind of structure formed by manganpyrosmalite, a silicate mineral with chemical formula Mni2FeMg3(Sii203o)(OH)ioClio. Give the oxidation state of each atom in this formula unit. 

Feldspars. Like the silica minerals, feldspars are framework silicates with all tetrahedral corners shared. By replacing one in four of the Si atoms by Al, the anionic framework Si3A10g is obtained from Si02 If the framework charge is balanced by structural K, the formula of potassium feldspar, KSisAlOg, is obtained. This feldspar has two common structural polymorphs (different structures with the same chemical formula), orthoclase and microcline. If the charge is balanced by structural Na, the feldspar obtained is albite, NaSi3A10g. 

FIGURE 7.7 The crystal structure of garnet. The general formula is AsBsC004)3 where C is Si for the silicates. The B cation sits in an octahedral site while the largest cation A is located in a dodecahedron. The bcc unit cell has a lattice parameter of -1.1 nm. With 20 atoms in the chemical formula there ate 160 atoms in the unit cell. 

Explain how the bonding and structures of silicates relate to their chemical formulas and properties (Section 22.10). 

So far, a total of about 200 distinct species of rare earth minerals have been described. A large number of carbonates, phosphates, silicates, niobates, fluorides, etc. are known as rare earth minerals. However, no sulfide of the rare earths has been reported as a mineral species. The rare earth minerals are defined as minerals containing rare earth elements as essential constituents (Levinson 1966). However, in order to judge this criterion, it is necessary to obtain structural as well as compositional information about the mineral. In addition, the determination of a chemical formula for a mineral also requires structural information in many cases, because order or disorder of certain atoms in the crystal structure cannot be determined by chemical analysis alone. Therefore, minerals with significant contents of rare earths are treated as rare earth minerals in this text, even if the rare earth content appears unessential to the mineral. 

Tranquillityite is from the Sea of Tranquillity on the moon (Lovering et al. 1971). The chemical formula suggests an interesting substitution between zirconium and yttrium. The crystal structure is unknown. Gatehouse et al. (1977) found that tranquillityite has a fluorite-related structure from their single crystal work using reconstituted samples in both air and vacuum, and that the structure is related to the structure of a MnZrTi-silicate synthetic phase. 

Analyze A mineral is described that has a sheet silicate structure with Mg " " and OH ions to balance charge and 1.5 Mg for each 1 Si. We are asked to write the chemical formula for the mineral. 

HNTs are different from MMT nanoclays with respect to their fundamental structure. Consisting of an octahedral aluminum layer and a tetrahedral silicate layer with a hydrated characteristic, HNTs are also known as 1 1 phyllosUicate.. Similar to a coil, the structure of HNTs is in the form of multilayered tubes rolled up by layers of aluminosilicates as observed in Figure 6.3. HNTs belong to the kaolin famUy with a chemical formula of Al2Si205(0H)4 H20 (Liu et al., 2007). HNTs are naturally abundant and available as hydrated clays with n = 2 for the water content. In general, the evaporation process of natural kaolin leads to the HNT structure (Lvov and Abdullayev, 2013). Lvov and Abdullayev (2013) also found the HNT length is approximately 0.5—2 pm whereas the inner and outer diameters are about 10—30 nm and 50—70 nm, respectively. Moreover, ecofriendly HNTs have become more cost competitive when compared with CNTs. Their unique cylindrical tubular... 

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