Final answer:
The source of the soil mineral content is the parent material. It is part of the C horizon in a soil profile and substantially influences the soil's structure and composition, providing nutrients vital for soil fertility.
Step-by-step explanation:
The parent material is the source of the soil mineral content. In a soil profile, the C horizon or soil base includes the parent material, which consists of organic and inorganic material that is broken down to form soil. This can be either created in its natural place or transported from elsewhere. The parent material is significant as it influences the soil type through its texture and provides nutrients to the soil. Over time, as soils develop, the parent material may become less recognizable due to weathering but still plays a crucial role in soil composition and structure.
Regarding the query about the different soil horizons, the topsoil is referred to as the A horizon, which is rich in organic material. The subsoil corresponds to the B horizon, which has an accumulation of mostly fine material that has moved downward from the A horizon, forming a denser layer in the soil.