Owing to the absence of readily available certified particulate reference materials (RMs), most analytical methods used to determine particulate contaminant levels in workplace or other environments are validated using solution RMs, which do not assess the robustness of the digestion step for all forms and sizes of particles in a sample. A library of particulate RMs having a range of chemical forms and particle sizes is needed to support a shift in method evaluation strategies to include both solution and particulate RMs. In support of creating this library, we characterized bulk and physically size separated fractions of beryllium oxide (BeO) particles recovered from the machining fluid sludge of an industrial ceramic products grinding operation. Particles were large agglomerates of compact, crystalline BeO primary particles having diameters on the order of several micrometers. As expected, the particle surface area was independent of sieve size, with a range from 3.61 m2/g (53-63-Ám fraction) to 4.82 m2/g (355-600-Ám fraction). The density was near the theoretical value (3.01 g/cm3). The data support more detailed characterization of the sludge materials for use as size-selective RMs. This work illustrates an approach that can be used to develop RMs that are difficult to digest.