The rarest of the great coloured stones
Fine untreated ruby is scarcer than any comparable diamond. Roughly 95% of ruby reaching the market has been heat treated, and of stones submitted for the top red designation only about 5% qualify. East Africa now supplies most of the world’s fine untreated ruby, and the material coming out of it is the reference against which the current market prices.
The reference colour is a narrow window of pure red with a faint blue secondary hue. Montepuez in northern Mozambique, in production since 2009, has proved capable of stones in the finest colour grades at sizes the older deposits rarely produced, and a clean unheated Montepuez stone above five carats with a top-tier origin report is now among the harder things in the trade to source.
Above three carats, untreated ruby stops behaving like a commodity. Clean natural stones at that size are genuinely rare, per-carat prices accelerate faster than for almost any other coloured gem, and each stone is judged entirely on its own merits.
