Geophysics aims to image subsurface geologic structure and identify different geologic units. While the former has dominated the interpretation of applied geophysical data, the latter has received much less attention. This appears to have persisted despite applications such as those in mineral exploration that inherently rely on the inference of geologic units from geophysical and geologic observations. In practice, such activities are routinely carried out in a qualitative manner. Thus, it is meaningful to examine this aspect and to develop a system of quantitative approaches to identify different geologic units. The development of geophysical inversions in the last three decades makes such interpretation tools possible. We refer to this newly emerging direction as geology differentiation and the resultant representation of geology model as a quasi-geology model. In this article, we will provide an overview of the historical background of geology differentiation and the current developments based on physical property inversions of geophysical data sets. We argue that integrating multiple physical property models to differentiate and characterize geologic units and work with the derived quasi-geology model may lead to a step change in maximizing the value of geophysical inversions.