There are several sites in the world where diatom microfossils have been detected in soil deposits (e.g., Mexico City, Mexico, and Osaka Bay, Japan). These natural soil deposits have singular physical and mechanical properties that do not follow the well-established empirical relations. However, the specialized literature on the topic is scarce. The unicellular algae known as diatoms are outstanding examples of micro- and nanostructured material in nature that may control mechanical and hydraulic properties of soils. However, comprehensive studies on interaction between diatoms, clay particles and water are non-existent. While diatoms are used in many engineering and scientific applications, very few geotechnical applications utilize diatoms. Yet, given their unique characteristics, there is great potential for utilizing diatoms in the development of engineered particulate materials for geotechnical and geoenvironmental applications. Simple shear tests were performed in this study to investigate undrained shear strength of artificial mixtures of diatomite-kaolin. The tests results indicate that the stress-strain curves show different characteristics depending on diatom content. Taking into account the presence of diatoms microfossils in Mexico City sediments, some of their unique engineering properties can be well explained.