An apparatus including an electromagnetic radiation source that emits electromagnetic radiation, a sample chamber comprising a fluid sample inlet for introducing a solids-laden fluid sample therein, and a detector that receives a backscattering signal and generates an output signal corresponding to a concentration of solids in the solids-laden fluid sample. The electromagnetic radiation transmits through the sample chamber and optically interacts with the solids-laden fluid sample to generate a backscattering signal. The sample chamber may include one or more of a shear bob for applying a shear rate to the solids-laden fluid sample, the shear bob suspended in the sample chamber and rotatable about an axis, a sealable fluid pressurizing inlet for pressurizing the sample chamber and a pressure gauge for measuring the pressure in the sample chamber when pressurized, and/or a temperature source for heating the solids-laden fluid sample.