There may be occasions when the USGS sends geologic materials to the contract lab that are inadequately prepared. In the event that this occurs, the contract lab will have to prepare these materials to the appropriate specifications. The materials will be ground in a pulverizer equipped with ceramic plates or a disc mill using an alumina corundum or agate chamber. All rock samples are ground to <200 mesh. All sediment and soil samples are ground to <150 mesh. All samples are mixed after preparation to ensure homogeneity for subsequent analysis.
Sample preparation is an important step in the analytical process. Without careful preparation and attention to inter-sample contamination, the worth of the subsequent analyses may be compromised. Therefore, all sample preparation equipment must be cleaned with pure, fine-grained silica sand between samples to avoid cross-contamination.
Central Mineral and Environmental Resources Science Center