1 · Constitute a composite sample
Distribution of the lot
Neighborhoods and choice of opposite pair
Keeping two opposing quarters approximately reduces the mass by half. The other two are stored in reserve. Homogenize again before each division; choosing a pair based on its content would introduce a bias.
Assumptions and reference
Discrete simulation with fictitious Cu/Co contents: mixing changes the spatial order of the units, without changing their mass or their composition. Without mixing, units remain grouped by zone. The units all have the same mass: this model does not predict the fundamental sampling error, nor the effects of particle size, humidity, density or dust. The target mass is not a guarantee of representativeness.
Division into four is an educational diagram of coning, flattening and quartering. A sampling procedure must be adapted to the material and the analytical objective.
USGS · Sample homogeneity and division