Crystal, habit halides

Figure 3.33 (a) Preferential adsorption of water molecules at the 111 faces of silver halide crystal, (b) Transformation of crystal habit from cubic 100 to octahedron 111 due to solvent adsorption. (Reprinted with permission from J.W. Mullin (1993), Crystallization, 3rd ed., CRC Press, to CRC Press Inc.. Boca Raton, Florida.)... 

Sylvite (syn., sylvinite) [7447.40-7] [Named after the Dutch chemist and physician of Leyden, Sylvia de la Boe (1614-1672)] (ICSD 22156 and PDF 41-1476) KCl M = 74.551 52.45 wt.%K 47.55 wt.% a (Halides) Coordinence K(6) Cubic fls 629.31 pm Bl,cF8 (2 4) S.G. Fm3m P.G.4-32 Rock salt type Isotropic n = 1.490 2.0 1988 Habit massive, cubic euhedral crystals, fibrous. Color white, yellowish white, reddish white, bluish white, or brownish white. Luster vitreous, greasy. Diaphaneity transparent to translucent. Streak white. Geavage (100), (010), (001). Fracture uneven, brittle, sectile. Soluble in water, the soln. color the flame of a bunsen in violet. Bitter taste. Fusible (m.p. 778°C). 

When silver halide crystals with a cube habit are exposed to electrons, photolytic metallic silver specks are formed in situ in an epitaxial relation to the silver halide substrate. This gives rise to moire fringes parallel to the cube edges due to the difference in lattice spacing between AgCl and Ag (Fig. 72). 

Several of the structure types found for the halides are observed for other important monovalent anion systems such as the trihydroxides and trihydrides and derivatives of these structures are observed for a variety of ternary phases (Haschke, 1975c and 1976b). Other monovalent anions, Y, are accommodated in PuBt3- and UCh-type RX3 phases by replacement of the X layers. The resulting RX2Y compositions are structural derivatives of the parent trihalide structures. These observations and the phase equilibria and crystal growth habits of the ternary derivatives support the conclusion that several of the trihalide structures are accurately described by alternation of RXj and X layers, but additional work is clearly necessary. 

N. Radenovic, W. van Enckevort and E. Vlieg. Eormamide adsorption and habit changes of alkali halide crystals grown from solutions. J. Cryst. Growth 263, 2004, 544. 

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