Mineral weathering is the major source of most essential nutrients including potassium (K). Biological factors are important in potassium release from K-bearing minerals. The objectives of this research were to investigate the effect of plant type and endophyte fungi on potassium uptake from phlogopite and muscovite and to study the mineralogical changes influenced by different plant rhizospheres. A pot experiment was carried out under greenhouse conditions in a completely randomized design with factorial combinations and three replications. Barley, alfalfa and tall fescue were tested in this study. The culture medium was a mixture of quartz sand (as the filling material) and phlogopite or muscovite. Pots were irrigated with distilled water and complete or K-free nutrient solution during a period of 140 days. At the end of the experiment, shoots and roots were harvested and their K concentration was determined. Clay-sized particles were analyzed using an X-ray diffractometer. Effect of plant type, culture medium and nutrient solution on shoot and root dry weight, potassium concentration and potassium uptake was significant. Under the K-free nutrient solution, phlogopite as a trioctahedral mica could easily provide enough K to all the three crops and the K concentration in barley and alfalfa was sufficient, whereas the K concentration was below the sufficient limit in tall fescue. But muscovite as a dioctahedral mica could not supply enough K for plants. Among the crops tested, the highest K uptake under K-free nutrient solution and in pots amended with phlogopite was recorded for barley followed by alfalfa and tall fescue. There was a statistically significant difference in K uptake between E + and E - tall fescue plants in phlogopite amended pots under the K-free nutrient solution. The strong vermiculitization of phlogopite was attested under both nutrient solutions, but with a much higher rate in the pots treated with the K-free nutrient solution. The rate of mineral transformation was greatly affected by plant type and endophyte symbiosis. Root system and their excretions are important factors creating differences in K uptake and mineralogical changes among crops. Effects of plant type and endophyte symbiosis on pH values were significant. This confirms the positive effect of the type and quantity of plant roots secretions on mineralogical transformations. Endophyte fungi symbiosis affected the plant excretions and increased the rate of non-exchangeable and structural K release from micaceous minerals. In addition to vermiculite, smectite and chlorite were detected as newly formed minerals in phlogopite amended pots. Also, a very weak vermiculitization of muscovite was recognized. These results Key words: Phlogopite, Muscovite, Endophyte fungi, Vermiculite, X-ray diffraction