Spodumen structure

The color of spodumen can vary from pale pink for the kunzite variety to a deep green for the hiddenite variety, but colorless crystals also exist. The green color of hiddenite is connected with Cr substituting for AP+, while also takes part in optical absorption spectrum formation. The green-yellow color of spodumen is connected with Fe " in the Ml position and Fe " in the M2 position. Pink color of kunzite is connected with Mn " impurities in different structural positions Ml and M2 (Platonov et al. 1984). 

FIGURE 7.11 The crystal structure of a pyroxene (spodumene) shows layers of Li+ (larger) and AP (smaller) ions in octahedra alternating with layers of Si in tetrahedra giving a nominal formula of LiAISisOe. 

D) Structures Derived from Keotite (6-Spodumene Solid Solution)... 

Skinner and Evans (1960) initially investigated the stability of LiAlSi20g P-spodumene. A frill crystal structure refinement by several authors indicated a space group P4j2j2. P-Spodumene has an obvious channel structure, and ionic conductivity reflects this structural feature. The conduction is thermally activated with an activation energy... 

The structure of P-spodumene is described in Section 1.2.1 in connection with the structurally related thermal properties. The solid solution P-spodumene ranges between n = 4 and n = 10 for Li20 Al203 Si02. The effect of the increasing Si02 content in the solid solution on the thermal expansion is shown in Section 1.3.1. 

This type of cellular membrane microstructure can be developed in glass-ceramics that exhibit a very low coefficient of thermal expansion because of the precipitation of p-quartz solid-solution or P-spodumene crystals (Beall 1992). The glass matrix, which is very thin and surrounds the crystals, plays the part of the cellular membrane. As a result, the crystals are separated from each other. The membrane accounts for approximately 10 vol% of the micro-structure and can, for example, act as a diffusion barrier between the crystals. 

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