Sorry for creating confusion. Let me try to explain another way.

Lets consider the following simplistic hypothetical example.

We have a rock which is composed of only two minerals, chromite and mineral Y. We don't know the proportions of either in the rock. but we do know, however, that mineral Y contains no Cr. We assay the rock and discover that it analyzes 25 wt % Cr2O3. How much chromite by weight must be in the rock to produce that assay? To determine that, we need to know the composition of the chromite grains themselves. We could accomplish this by either producing a 100% chromite concentrate and analyze it for Cr, or analyze individual chromite grains by microprobe. We choose the latter and find that the analyses of the individual grains are uniform at 50% Cr2O3. So if a rock assays half that much, then the rock must contain 50% by weight chromite of that composition. It follows that the higher the Cr content of the chromite grains, the higher the Cr assay of the rock if the rock still contains 50% chromite, and vice versa. Thus the Cr assay of the rock reflects not only the % chromite in the rock, but simultaneously the Cr content of the individual chromite grains.

In other words, to convert a rock Cr2O3 assay into an estimate of the proportion of chromite in the rock, we need to know the composition of the chromite grains per se. This information is critical when considering beneficiation or up-grading to a concentrate for further processing or sale.

Hope this helps

Regards

geoprof