07 September 1990
Vol 249, Issue 4973

About The Cover

Photomicrograph of Hawaiian xenolith showing layers of cumulus spinel (black) and olivine (colored) grains, and intercumulus garnet (deep purple) in the spinel layer. This photo was taken with crossed polars and gypsum plate inserted. Vertical field of view is 65 millimeters. See page 1154. [Photograph by Gautam Sen. This xenolith is part of the Dale Jackson Collection (Smithsonian Institution)]