Orthopyroxene and clinopyroxene (diopside) in lherzolite

Click on image to enlarge.          Photo © Daniel R. Snyder

Pale yellow grains are pyroxenes. Lower pyroxene grain is orthopyroxene, upper grain (actually several contiguous smaller grains) is clinopyroxene. When the stage was rotated, the orthopyroxene grain showed parallel extinction, the clinopyroxene grain - inclined extinction. However, there is also a morphological difference in this case: the orthopyroxene grain has a more regular, parallel cleavage pattern, while the clinopyroxene  has shorter, curving, and kinked cleavage cracks. Bright-colored grains are olivine, black areas are grains at extinction and voids. Cr-diopside lherzolite mantle xenolith. San Carlos Indian Reservation, Arizona. XPL. Imaged area 1.3 mm x 2 mm.