Types of Mechanical Weathering Frost wedging – water penetrates into cracks, expands when it freezes. Must have: Adequate moisture Cracks in rocks Freeze/thaw cycles
Types of Mechanical Weathering Salt wedging – growth of minerals in cracks Desert environments Water evaporates, ions in solution combine to form minerals
Types of Mechanical Weathering Biological wedging – plant roots penetrate into cracks causing cracks to widen. Must have: Climate hospitable for plants Adequate moisture and temperature
Unloading removal of pressure of deep burial
repeated daily heating and cooling of rock; heat causes expansion; cooling causes contraction. Thermal expansion
Chemical Weathering Results in new minerals and ions in solution. Chemical alteration of minerals. Water and acid are essential.
Types of Chemical Weathering 1.Ion Exchange – H+ replaces other cations. 2.Dissolution - mineral completely dissolves, leaving only ions in solution. 3.Oxidation - reaction in which elements gain or lose electrons (example: rust). Hydrolysis - any reaction in which water participates.
Carbon dioxide reacts with water to form carbonic acid (Equation 1). Carbonic acid then dissociates to give the hydrogen ion (H+) and the hydrogen carbonate ion (HCO 3 -) (Equation 2). The ability of H 2 CO 3 to deliver H+ is what classifies this molecule as an acid, thus lowering the pH of a solution.