Small angle light scattering was used to study the structures of aggregates and aggregation kinetics of silica and hematite particles. The fractal dimensions of silica aggregates were found to vary between 1.76 and 2.30, depending on the solution chemistry. These values encompass the range of theoretical values from diffusion limited cluster aggregation (DLCA), through to reaction limited cluster aggregation (RLCA) with spontaneous restructuring. Under different experimental conditions, the aggregation kinetics exhibit a variety of behaviours. Small angle light scattering experiments performed on aggregating mixtures of hematite particles of two different sizes showed significant high q deviations from typical q^-Df scattering behaviour for fractal aggregates. The deviation was also observed in simulations and can be explained in terms of reduced partial fractal scattering amplitude from heavy particles distributed in the aggregate.