Colored gemstones occupy a world more complex, less standardized, and potentially more rewarding for knowledgeable buyers than diamonds. Ruby, sapphire, and emerald — the traditional Big Three — each have unique quality factors, origin premiums, and treatment norms.
Ruby and sapphire are both the mineral corundum (Al2O3). The color difference comes from trace impurities — chromium makes corundum red (ruby), iron and titanium make it blue (sapphire). These trace elements substitute for aluminum in the crystal lattice at concentrations below one percent. They are the entire difference between a $5-per-carat opaque corundum and a $50,000-per-carat pigeon blood ruby.
Origin is the critical value factor in colored gemstones. A one-carat unheated Burmese ruby might sell for $15,000 to $30,000. A one-carat unheated Mozambican ruby of similar quality might sell for $5,000 to $10,000. The difference is not quality — the Mozambican stone may be cleaner and better cut — but provenance. The Burmese origin carries a premium reflecting both the historical prestige of the Mogok mines and current supply constraints on Burmese material entering Western markets.
Emerald forms in a rare geological setting: beryllium-bearing pegmatites intruding into chromium-rich rocks. Beryllium is rare, chromium is concentrated in specific rock types — their coincidence in one location is geologically uncommon, which is why emerald deposits are so scarce and production so concentrated. Colombia, Zambia, and Brazil account for the vast majority of gem-quality emerald.
Most colored gemstones undergo treatment. Ruby and sapphire are routinely heat-treated — heated to high temperatures under controlled conditions to improve color and clarity. This is standard industry practice, accepted without disclosure in most markets. Emerald is almost universally oiled or resin-filled to mask surface-reaching fissures. The quality of the treatment varies enormously between dealers. The buyer's protection is laboratory certification: a report from GRS, GIA, AIGS, or Gubelin specifying any detected treatments.