Interference color is often a key diagnostic criteria for mineral identification. In thin section , the thickness is uniform, thus the interference color is dependent on the birefringence and orientation of the mineral. The result if that portions of the mineral are in different orientation. Twins consist of segments of the mineral that usually go extinct at different positions with stage rotation. Twinning is a diagnostic feature used to identify many minerals.
Feldspars are the most commonly observed minerals in soils that are twinned.
Common in albite, plagioclase feldspars, sometimes thin lamellar twins seen in large calcite and dolomite crystals, but rarely in pedogenic calcite. Characteristic of microcline. The perthite pattern may take several forms. Imperfect reaction between the solid phase and liquid phase may result in zoning. Zoning may take several forms.