3a. Why do rocks formed at greater depths weather easily under surface conditions?
b. With equations, state what is leaching
c. What are the residual minerals of Quart, Fe-Mg minerals and calcite after weathering?
a. Rocks formed at greater depths are typically under high pressure and temperature conditions. When these rocks are exposed to surface conditions, they experience a significant change in pressure and temperature. This change can cause the rocks to expand and contract, leading to the development of cracks and fractures. Additionally, the decrease in pressure and temperature can result in the breakdown of certain minerals within the rocks, making them more susceptible to weathering processes.
b. Leaching is a process in which water or other solvents dissolve and remove specific minerals or substances from a solid material. It is represented by the following equation:
Solid mineral + Solvent → Soluble mineral + Solution
The dissolved minerals are transported away from the solid material, leaving behind a residue or leachate.
c. The residual minerals after weathering of quartz, Fe-Mg minerals, and calcite can vary depending on the specific weathering conditions. However, common residual minerals are:
- Quartz: Quartz is highly resistant to weathering and tends to remain as residual minerals after weathering. It is chemically stable and does not easily react with water or other weathering agents.
- Fe-Mg minerals: These minerals, including various iron and magnesium-bearing minerals like olivine, pyroxene, and amphibole, can undergo chemical reactions with water and oxygen during weathering. The exact residual minerals will depend on the specific weathering conditions, but commonly, iron and magnesium oxides or hydroxides (such as hematite or goethite) may be formed.
- Calcite: Calcite is a type of carbonate mineral and is relatively soluble in water. It can be easily weathered and dissolved under certain conditions, leaving behind residual minerals such as clay minerals (e.g., kaolinite) or other forms of calcium carbonate (e.g., aragonite or limestone).