Yes, but such has been found in an outer ring of an impact crater in Canada. They would have once been a possible source of tiny industrial diamonds but with the manufactured diamonds available today they’re not economically mined.
How would the diamonds be separated? Are they all just fused together by rock? If that’s the case, then maybe solvents could dissolve the rock. I don’t know if heat would work because diamonds, I believe, can actually burn, being carbon. Would depend on the required temps I guess. It would be fascinating if you could just heat up the entire encrustation and strain out the liquid rock, leaving the diamonds behind.