Factors for residual soil characteristics

The characteristics of a residual soil depend on:

1. Parent rock: type and mineral composition (granite gives sandy soil; basalt gives clayey soil).
2. Climate: temperature and rainfall control the rate of weathering; warm humid climates cause deep chemical weathering.
3. Topography: gentle slopes keep the weathered material in place; steep slopes remove it.
4. Time: the longer the weathering, the deeper and finer the soil.
5. Drainage and groundwater: leaching removes soluble minerals.
6. Vegetation and biological activity: add organic matter and acids.
7. Rate of removal: weathering rate must exceed the erosion rate for residual soil to build up.