Twinning Definition Twinning is the observed intergrowth of multiple crystals in a symmetrical fashion. This term applies to the examination of rock thin sections, in the field of optical mineralogy.

Oblique-Slip Fault Oblique-Slip Fault: In geology, an oblique-slip fault is a fault that moves parallel to the strike or dip of the fault plane.

Rock Stratigraphic Unit In the field of geology, a rock stratigraphic unit, or a lithostratigraphic unit, is a geologic formation that is identifiable by a specific lithology, as well as a consistent stratigraphic position. For example, the Monterey Formation is a rock stratigraphic unit, as it tends to consistently comprise the same gravel and sand…

Degree of Saturation (SR) “Degree of Saturation” (SR) is an engineering geology term and refers to the ratio of the volume of water to the total volume of void space. The Degree of Saturation or SR-value ranges from 0% to 100% (0% being completely dry, and 100% being fully saturated). Degree of Saturation Formula Degree…

Hardpan (Caliche) “Hardpan” is a highly dense and solid layer of soil near the ground surface, which is usually comprised of clay or silty-clay soils. Hardpan forms by cementation over time, during the process of precipitation of insoluble substances such as calcium carbonates, silica, iron oxides, and other organic matter. “Hardpan” is a term mostly…

Mafic Definition In geology, “mafic” is a term that describes an igneous rock that has an abundance of darker color minerals.