Good sub-sampling technique becomes important when the large sample is not homogeneous.
Coning and quartering is a method used by analytical chemists to reduce the sample size of a powder without creating a systematic bias.
The technique involves pouring the sample so that it takes on a conical shape, and then flattening it out into a cake.
The sample is dropped into the top, and the box produces two equally divided subsamples.
Riffle boxes are commonly used in mining to reduce the size of crushed rock samples prior to assaying.