Silicate, chemical formula

Chemical/Pharmaceutical/Other Class Silicate Chemical Formula Mg3Si40io(OH)2... 

LS lanthanum silicate. Chemical formulae or abbreviations denote the primary phase volumes. The thick arrow shows the stoichiometric composition of langasite. (Reproduced by the permission of Elsevier Ltd.)... 

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... 

Similarly to Mn(IV)- and Fe(III)-oxides, some primary minerals were shown to promote polymerization of hydroquinone (19). Olivines, pyroxenes, and amphiboles accelerated the polymerization reaction to a greater extent than micas and feldspars. Microcline and quartz were ineffective- The effect was greatest for tephroite, a manganese-bearing silicate with the ideal chemical formula M SiO. Fayalite, the corresponding Fe(II) analog (Fe2Si0 ), was effective, but to a lesser extent. 

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. 

Zeolite minerals are hydrous-aluminum-silicates whose general chemical formula can be expressed as... 

What is the chemical formula of a potassium silicate in which the silicate tetrahedra share (a) two O atoms or (b) three O atoms and form a chain In each case, there are single negative charges on the unshared O atoms. 

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). 

Actinolite— A mineral in the amphibole group, a calcium magnesium (iron) silicate with the chemical formula Ca2(Mg,Fe)5Sig022(0H)2. The mineral occurs as a series in which magnesium and iron can freely substitute for each other. Actinolite is the intermediate member when iron is predominant the mineral is ferro-actinolite and when magnesium is predominant, the mineral is tremolite. The iron produces a green color that darkens as the iron content increases. Actinolite may occur in fibrous form (an asbestos). It is not used commercially, but is a common impurity in chrysotile asbestos. 

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. 

Analyzing data Give the chemical formula for the latex (isoprene) monomer and the ethanol-sodium silicate polymer. 

The most abundant and important of the aluminosilicate minerals in the earth s surface are the feldspars, which result from the substitution of aluminum for silicon in three-dimensional silicate networks such as quartz. The Al ions must be accompanied by other cations such as sodium, potassium, or calcium to maintain overall charge neutrality. Albite is a feldspar with the chemical formula NaAlSi308. 

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. 

To help understand the discussion on weathering, a veiy brief review of the names and chemical formulae for some of the important rock-forming minerals is presented here. The silicate discussion is mainly from Drever (1982). 

Only K, B, H, S and R were used as sourees of data for simple oxides, oxohydroxides and hydroxides. Specialized databases created primarily for mineralogists and geologists report on thermodynamic data for materials of their special interest, e.g. natural silicates and aluminosilicates. These databases were used to complete data which were not available in K, B, H, S or R. Ref. [14] abbreviated as C does not directly list G° or AGf values. The G° values were calculated from Eq. (2.28) using the S taken from C. Then, Eq. (2.26) was applied to calculate AGf (compound) and the values of G° (elements) were taken from K. Then, data from Ref, [15] abbreviated as P were used. A few chemical formulas in P have typographical errors, which have been corrected in Table 2.2. The G° values were... 

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. 

A crystal is an arrangement of ions or atoms that is repeated at regular intervals in three dimensions. The smallest repeating three-dimensional array of a crystal is called the unit cell. The unit cell dimensions a and b (the x and y dimensions) are constant for a given mineral the c (or z) dimension is also constant, except for the special case of swelling layer silicates (Fig. 5.3). The basal plane is the a-b plane. The chemical composition of layer silicate minerals is normally expressed as one-half of a unit cell, to simplify the chemical formulas. 

Amphibole A group of chain silicates. The simplest chemical formula for an amphibole is Ca2Mg5Si8022(0H)2. 

The naturally-occurring form of magnesium silicate hydroxide is called talc, a soft mineral that feels waxy and soapy to the touch. This characteristic has led to another name for the mineral soapstone. Talc s chemical formula differs somewhat from that of magnesium silicate hydroxide Mg3Si40lo(0H)2. 

---