Martian 'pebbles' don't prove watery past NASA probe could be walking on broken glass.
From Nature:
Martian 'pebbles' don't prove watery past
NASA probe could be walking on broken glass.
10 February 2004
MARK PEPLOW
NASA's Spirit and Opportunity rovers continue to send back photos from Mars, some offering tantalising geological evidence that water once flowed across the red planet's surface. But researchers caution that there are other explanations...
http://www.nature.com/nsu/040209/040209-2.html