If mini-bulk sampling recovers a significant number of commercial-sized diamonds, progressive stages of bulk sampling are required in order to estimate the grade and average value of the diamonds to establish economic value of the kimberlite pipe. Sampling a wide area of the pipe is necessary in order to obtain a representative understanding of the diamond content of the entire body.
Diamonds recovered at this stage are studied and evaluated for size, clarity, and colour to determine the average market value. A typical population of diamonds recovered from an economic kimberlite contains the entire range of diamond quality, from industrial, through to top gem-quality. Because gem-quality diamonds are considerably more valuable than near-gem or industrial diamonds, the number of diamonds in the kimberlite can be less important than their quality. Therefore a low-grade kimberlite with a high proportion of gem-quality stones can be more valuable than a high-grade kimberlite with a low percentage of gem-quality diamonds.