Structure of Quartz

Crystal structure of quartz. The Si (gray) and 0 (red) atoms form six-membered rings. Each Si atom is bonded telrahedrally to four 0 atoms. 

Dislocation lines do not move concertedly, that is, all at once. They move, by forming kinks along their lengths, and when the kinks move, the lines move. The open crystal structure of quartz (crystobalite) results in a relatively large amount of volume being associated with a kink on a dislocation line. This relatively large volume lowers the value of quartz s bond modulus, making its hardness consistent with those of other covalently bonded substances. 

Wilding et al. (1977) showed that the sihca tetrahedron in quartz is almost sym-mehical and has a Si-O distance of 0.16nm. They noted that the structure of quartz can be visualized as a spiral network of silica tetrahedra around the z-axis. From... 

Figure 1.44 The structure of quartz, showing the three-dimensional network of Si04 tetrahe-dra. Reprinted, by permission, from L. G. Berry, B. Mason, and R. V. Dietrich, Mineralogy Concepts, Descriptions, Determinations, p. 388, 2nd ed. Copyright 1983, Freeman Publishing, Inc.

FIGURE 7.2 The structure of quartz (a) as a ball and stick representation and (b) as linked [S104] tetrahedra. 

Quartz crystals are composed of silica, Si02. When the silica is pure, as here, it is colorless. The internal structure of quartz is highly complex, but can be pictured in terms of tetrahedral Si04 units, linked through shared oxygen atoms. When quartz crystals melt and solidify again, they may form an amorphous material known as a glass, in which the tetrahedral units form a more random jumble. 

The PCs bind only a small portion of carbon atoms that are built into the structure of quartz glass during the preparation of RSi. The EPR-detected... 

Top) The structure of quartz (empirical formula Si02). Quartz contains chains of Si04 tetrahedra (bottom) that share oxygen atoms. 

The structure of quartz, which has the empirical formula Si02. Note that the structure is based on interlocking Si04 tetrahedra, in which each oxygen atom is shared by two silicon atoms. 

FIGURE 5.16. Structure of quartz, Si02, showing (a) a stereoview and (b) an indication of atomic identities in the helical packing in levorotatory quartz. 

The X-ray structures of quartz and calcite were obtained from the FIZ Karlsruhe ICSD database [76]. The chosen model structures were constructed in MATERIALS STUDIO [77] under periodic boundary conditions and were then energy-minimized using the program DISCOVER with COMPASS force field until a maximum derivative better than 0.01 kcal mor A was achieved. 

Covalent network solids Atoms such as carbon and silicon, which can form multiple covalent bonds, are able to form covalent network solids. In Chapter 7, you learned how the structures of graphite and diamond give those solid allotropes of carbon different properties. Figure 13-20 shows the covalent network structure of quartz. Based on its structure, will quartz have properties similar to diamond or graphite ... 

FIG. 23.6. Plan of the structure of/ quartz. Small black circles represent Si atoms. The oxygen atoms lie at different heights above the plane of the paper, those nearest the reader being drawn with heaviest lines. Each atom is repeated at a certain distance above (and below) the plane of the paper along the normal to that plane so that the SiaOa rings in the plan represent helical chains. 

The structure of quartz has been extensively studied [7-10], Table 2 summarizes structural data for low quartz obtained with the Accelrys Catalysis 3.0.0 software. The continuous connection of oxygen tetrahedra is apparent from its structure illustrated in Figs. 4 and 5 [11,13],... 

FIGURE 11.31 Two-dimensional representation of (a) crystalline quartz and (bj noncrystalline quartz glass. The small spheres represent silicon. In reality, the structure of quartz is three-dimensional. Each Si atom is tetrahedraHy bonded to four O atoms. 

Schlcgcl ML, Nagy KL, Fenter P, Sturchio NC (2002) Structures of quartz (010)- and (llO)-water interfaces determined by X-ray reflectivity and atomic force microscopy of natural growth surfaces. Geochim Cosmochim Acta 66 3037-3054... 

Figure 2.2 The structure of quartz, represented as (a) linked tetrahedra and (b) an extended molecule.

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