high-tiffany 1837 jewelry polymorph of cordierite

Interpretation of the optical properties of cordierites from Daimonji-yama, described above, was first presented by Kitamura and Yamada (1987); this discussion is based primarily on that work. The optical properties provide a great deal of information regarding the mechanism of formation of sakura ishi. The most obvious characteristic is that they are not single crystals but rather complex intergrowths of multiple crystals. In the center of these intergrowths is the apparent pinacoid sector (figs. 7, 14). The zigzag extinction texture of these is thought to result from the transformation of an original indialite crystal to cordierite. The structures of these two minerals are very similar and are related by the distribution of Si and Al among the tetrahedral sites. Indialite, the high-tiffany 1837 jewelry polymorph of cordierite, is hexagonal. In indialite the Si and Al are randomly distributed among the tetrahedral sites. When indialite cools below the transition temperature to cordierite, the Si and Al move into a Tiffany Metropolis Cuff links distribution among the tetrahedral sites (this is exactly analogous to the transition between the sanidine and microcline structures [Putnis 1992]). The transition temperature is dependent on the exact composition of the indialite and is about 700°C for the Daimonji crystals (Kitamura and Hiroi 1982; Kitamura and Yamada 1987). The process of an element going from a random to a nonrandom distribution in a crystal structure is called ordering. The result of ordering in this case is a lowering of the symmetry from hexagonal to orthorhombic, and thus the transition (phase transition) from indialite to cordierite. There are also small structural changes such as tiffany on sale rotation of the tetrahedra around their shared oxygens that occur in response to the redistribution of Si and Al. Ordering of Si and Al occurs such that the a-axis of the cordierite will be parallel to one of the three equivalent a-axes of the original indialite (fig. 14b). This ordering can start independently at different points within the indialite, and areas (domains) of all three equivalent orientations will form. Once a domain of a particular orientation starts, it will spread outward until it hits another domain. The end result is an intergrowth of cordierite domains, each with one of three crystallographic orientations related by a 120° rotation to each other, and thus different extinction orientations in crossed polars, as is observed here (fig. 14). The intergrown domains of cordierite are in a pseudotwin relationship (Kitamura and Hiroi 1982; Kitamura and Yamada 1987). The indialite to cordierite transformation texture is found in the central core of the sakura ishi as well as throughout the entire apparent pinacoid sectors. This geometry is fully discussed below and shown in figure 18.


The transformation texture observed in the apparent pinacoid sectors is not observed in the six apparent prism Frank Gehry jewelry. This indicates that these grew directly as cordierite and were not the result of a transformation from indialite. The specific orientational relationship among the six cordierite crystals was interpreted by Paloma Picasso Loving Heart earrings and Yamada (1987) to result from the epitaxic overgrowth (see Word to the Wise, this issue) of cordierite on six {100} faces of an original indialite crystal (fig. 15).


The apparent sectoral morphology of sakura ishi (fig. 7), and the indialite to cordierite transformation texture found throughout the apparent pinacoid sectors, indicate that once the cordierites had epitaxicly nucleated on the six {100} faces of the indialite, the indialite continued to grow concurrently with the cordierite discount tiffany money clips. Because the prism faces of the original indialite were covered by the growing cordierite crystals, continued growth of the indialite could only occur on its pinacoid faces (fig. 15). From this scenario an obvious question arises: If cordierite epitaxicly overgrew the prism faces of the original indialite crystal, why did it not do the same on the pinacoid faces of the indialite? As discussed in the Word to the Wise column, titled "Epitaxy," in this issue, the likelihood of epitaxy occurring is related to the degree of mismatch between the atomic structures of the substrate and the overgrowth. Thus, it is worthwhile to make a comparison of the cordierite structure to the indialite structure on the prism {100} and pinacoid {001} faces. The mismatch between the structures at the (100)^sub cordierite^ - (100)^sub indialite^ interface (fig. 16) is relatively small; thus, the energy barrier for cordierite to epitaxicly Tiffany Notes cuff and grow on the {100} faces of indialite is also relatively small. In contrast, the (001)^sub cordierite^ - (001)^sub indialite^ interface (fig. 17) exhibits a much greater degree of structural mismatch between the two phases. Hence, it is energetically less favorable for cordierite to nucleate on the {001} faces of indialite. It is suggested that this difference in the energy necessary for epitaxic nucleation of cordierite on the two different crystal forms of indialite is the reason that it only nucleated on the {100} faces.

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