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An introduction to minerals and rocks under the microscope

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Figure 44 (a) Garnet in its distinctive dodecahedral (12-sided) form, due to its cubic crystal structure (long diagonal of the crystal face is 3.4 cm across). (b) Plane-polarised light image of a garnet in garnet mica schist. Garnet is a high-relief mineral that can be faintly coloured, depending on its composition (field of view 5.5 mm across). (c) The same field of view as in (b) between crossed polars; garnet is isotropic so stays black when the thin section is rotated. The grey and transparent streaks and spots in the garnet are quartz crystals included in the garnet as it grew.

 3.3.2 Garnet