Unformatted text preview: 72x3 (Box 2) and TS—7 (Box 4). Sample 72x3 contains biotite (brown pleochroic). In
xpl examine how the mineral goes extinct when its cleavage planes are parallel to the
cross hairs of the microscope. In other words it goes extinct when the cleavage planes
are parallel to the polarizers. This is called parallel extinction. Now look at sample TS-7
and notice how the clinopyroxene goes extinct when the cleavage planes are at an angle
to the cross hairs and polarizers. This is called inclined extinction. Sketch both the clinopyroxene and biotite crystals showing parallel and inclined extinction. 72"3 m “rs-7 “a ohm—t. A etch-1041‘” 06 w.-.
. .. mining ...
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- Spring '09