09 August 1996
Vol 273, Issue 5276

About The Cover

Chondrule (850 micrometers in diameter) from the unmetamorphosed Chainpur meteorite, containing excess 26Mg from decay of 26Al 4.6 billion years ago. Initial abundance of 26Al is one-fifth of that in Ca-Al inclusions, the oldest solids formed in the solar system, implying that chondrules formed--and the solar nebula lasted--for more than 2 million years. The chondrule includes glass (dark magenta), brightly colored olivine and dendritic pyroxene, and blocky spinel (light magenta). See page 757. [Transmitted polarized light (plus gypsum plate) photo: G. J. MacPherson]