An investigation was made into dielectric properties of quartz crystals, brown-clay, grey-clay, whitish-clay and some rocks found in Uganda under temperatures of about 25ºC and pressure of approximately 66.0 cm of mercury. This study was conducted at Makerere University in Uganda some time back and revisited in 2009. The analysed materials were provided by the Department of Geology Entebbe, Ministry of Survey and Natural Resources Uganda. Measurements were carried out in the frequency range of 8.2-12.4 GHz, using circular cavities energized in the TM_01n family of modes; the signal frequency had no effect on, n, as this was not in the axis of propagation. The relation D = cx_n / (πf_c √∈_r) was used to calculate the dielectric constant ∈_r for cut-off frequency f_c, x_n is the n^th root of the first kind of the Bessel function J₁(x) = 0 and c is the velocity of light. The study revealed that in Uganda there are: (i) crystals of dielectric constant 0r in the range ∈_r = 4.48 - 4.57 and these values of ∈_r are close to that of Piezo-electric crystal whose ∈_r = 4.6, (ii) clays and black rock whose dielectric constants ∈_r = 1. The study revealed that when a raw material is put in a cavity its dielectric constant can be determined by observing the resonance or (absorption frequency). Material with higher dielectric constants had correspondingly lower frequency than those with lower dielectric constants.