The most important factor is the parent material that forms the soil sample. For instance, the bedrock and the layer above it determine the mineral content of the soil formed. If the bottom layer is too hard, it may take a considerably long period of time for weathering process to break it down.
The second important factor is the climatic pattern because it determines the type of natural agents of weathering available in a given region for the soil formation. In addition, the topography of the region under weathering process is important to consider. The weathering process is faster on the sloppy ground than on a flat one. Finally, biota and time factor in the process of soil formation is important. It takes a longer period of time to form tiny soil particles.