Chalk

From SCWiki

Magnesium Carbinate, first used for climbing by by gymnist climber John Gill, back in the early days of free climbing. used to absorb/disipate and evaporate sweat, and thereby give better grip on the rock. Overuse leads to gunk-filled holds, and low friction. Some chalk producers, such as Metolious, add powerfull drying agents, to enhance the effects of the chalk.

See also: Pof