07 June 1991
Vol 252, Issue 5011

About The Cover

Quartz crystal (530 micrometers across) from a peralkaline rhyolite containing several inclusions of silicate melt (now glass). These inclusions were used to study the volatility of copper in magmas. Experimental heating caused the boomerang-shaped inclusion to leak and exsolve vapor bubbles, whereas the large black inclusion at the bottom did not leak. Other intact inclusions contained rare, copper-rich bubbles, which are interpreted as magmatic vapor. See page 1405. [Photograph taken under crossed polars by J. B. Lowenstern]