We present small angle x-ray scattering data of single-domain nematic and columnar liquidcrystal phases in suspensions of sterically stabilized gibbsite platelets. The measurementsare performed with different sample orientations to obtain information about thethree-dimensional structure of the liquid crystalline phases. With the x-ray beam incidentalong the director of the nematic phase a strong correlation peak is observed correspondingto the side-to-side interparticle correlations, which suggests a columnar nematic structure.Upon sample rotation this side-to-side correlation peak of the nematic shifts to higherQ-values, suggesting the presence of strong fluctuations of small stacks of particles withdifferent orientations, while the overall particle orientation is constant. In the hexagonalcolumnar phase, clear Bragg intercolumnar reflections are observed. Upon rotation, theQ-value of these reflections remains constant while their intensity monotonically decreasesupon rotation. This indicates that the column orientation fluctuates together with theparticle director in the columnar phase. This difference between the behaviour of thecolumnar and the nematic reflections upon sample rotation is used to assign the liquidcrystal phase of a suspension consisting of larger platelets, where identification can beambiguous due to resolution limitations.