parent material

The underlying geological material from which a soil forms — the bedrock, glacial deposit, alluvium, loess, or volcanic ash that weathers and breaks down over centuries to produce the mineral fraction of the soil above. Parent material determines a soil's texture, mineral content, and drainage. Soil derived from granite is sandy and acidite; soil derived from limestone is alkalite and clay-rich; soil derived from basalt is dark and fertile. Every soil is its parent's child, and the resemblance shows.