In mining terms - weathered kimberlite that is economically...

In mining terms - weathered kimberlite that is economically viable is referred to as Yellow ground. Generally it is easier to mine as being friable and requires less crushing ( beware of the clay content). Blue ground on the other hand is pristine unweathered Kimberlite and displays a dark grey to deep blue colour. Like any rock it would need to be crushed to release the diamonds.

Early miners in Kimberley used to spread the yellow ground( called "flooring") brought to surface over huge tracks of land to accelerate the weathering process and thus eliminate any crushing.

Generally Kimberlite once exposed to the elements and moisture "exfoliates" and breaks up. Hope this helps.