Analysis and testing of powders for chemical assay and physical measurements, such as particle size, density and surface area, often requires reduction of a large sample quantity into smaller amounts. Therefore, it is necessary that the sub-sample ultimately analyzed shall be representative of the initial lot or batch for reproducible and valid data. The Rotary Micro Riffler easily and automatically divides larger samples into eight smaller representative samples for analysis. By repetitive division of the collected smaller representative samples, the desired final sample size may be obtained. The Rotary Micro Riffler has two basic components: A circular vibrating bowl which is amplitude-variable and controls the delivery rate of the initial sample powder. A sample collector which is a rotating disc holding eight test tubes. Size of the test tubes may be varied to accommodate the initial sample size. To accommodate a variety of materials the Rotary Micro Riffler has two sets of controls; one for the delivery rate and the second for the rotation rate of the collectors. By varying these two controls, accurate divisions of any powder may be achieved regardless of particle size or density.