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• 1. Structure
• 2. Plate Tectonics
• 3. Weathering
• 4. Rock Cycle
• 5. Soils

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3. Weathering

There are three distinct mechanisms of chemical weathering

The three different mechanisms in chemical weathering are: dissolution; acid hydrolysis; and oxidation. Various combinations of these occur simultaneously during most weathering processes.

	Feldspars Feldspars are weathered slowly by acid hydrolysis, and often develop a marked surface pitting. The pits represent parts of the mineral which are more soluble and are removed preferentially. Such sites occur where the crystal is imperfect, or has been strained. Weathering leaves behind a solid residue composed of clay minerals.
	Pyrite Pyrite weathers in contact with oxygen and water by mineral oxidation. The products are an acidic solution (sulphuric acid) and a red brown solid (iron oxide) which coats the surface of pyrite.
	Quartz Quartz is very resistant to dissolution and acid hydrolysis, and shows little or no change in appearance even with prolonged exposure to weathering.
	Calcite Calcite is dissolved relatively easily by acid hydrolysis and dissolution, often by the action of acidic solutions produced by dissolving atmospheric carbon dioxide in water. Weathering completely dissolves calcite, without leaving any solid residue.

Name the three different mechanisms which are important in chemical weathering.