Clay, Clay Minerals and Product Fines

In civil engineering, clay often means clay soil which contains clay (and other) minerals with plasticity and cohesive properties. Not all fine-grained soils are cohesive or classified as clays and examples of this are silts and rock flour which is typically produced from crushing quarry products. The particles of these materials are invisible to the naked eye and can be determined through specialised geochemical testing. X-Ray Diffraction (XRD) is a common test used to determine the different clay minerals as well as rock flour present and can provide a quantitative result.

The importance in knowing what makes up the fines content is that the presence of water sensitive (hydroscopic) clays and minerals can significantly affect the material engineering behaviour. These characteristics have noteworthy engineering significance for the use of quarried products such as road base, manufactured sands and fill material as well influencing potentially a dam or pipeline investigation where seams of clay have been identified within drill core.