1. Part 7 CHEMICAL WEATHERING PROMOTED BY PRECIPITATION OF SALTS

2. Lichens secrete acidic enzymes which can react with host rock, accelerating chemical weathering. This shows an assortment of lichens developed on granite in a humid environment in the Ouachita Mtns of Arkansas

3. Lichens and sponge moss growing on a carbonate-cemented sandstone. Moss absorbs and retains water, hastening the weathering process, causing a pitted texture.

4. Precipitation of sodium chloride from Vishnu Schist along Clear Creek in the Grand Canyon – a very arid environment

5. Precipitation of sodium chloride on Precambrian granite in the Gulf of Thailand – in the tropics.