>Expanding on Jos' statistical POV: the mine is one of how many producing more than one 600+ct stones in the last 40 years. Since the mine was closed for a stretch of time perhaps "in the last 30 yeras of active production" would even be more relevant. But the pure size makes it better understandable for those poor blokes still paying rates for the comparedly minuscule stones on engagement rings...

Which aren't that worth at all - just try to sell one yourself.

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