The rarest rubies are the ideal ones you see depicted in TV shows and films; a pure, red stone large enough where the rich heiress has trouble lifting her dainty hand.
The 4Cs are an excellent guide to the quality of a gemstone. The pure red color (the first C) is made by the presence of chromium in the ruby, and it does not take much to alter the color slightly. Rubies need a lot of chromium to be red, but only a little bit of iron and titanium to alter the color undesirably. Chromium is also a much rarer element than iron and titanium, making the pure red that much rarer.
R10375 | “Ruby ID: R10375”
R10006 | “Ruby ID: R10006”
R10018 | “Ruby ID: R10018”
Clarity, the second C, is the next quality factor. Rubies may be eye-clean, but magnification will often reveal characteristic inclusions like included crystals, partially healed fingerprints, needle-like crystals, tiny dots called pinpoints, and more. All of this stuff is in there because rubies form in a superheated, magmatic soup of whatever random elements are in the area. They only form in a very rare and unusual mixture of them, so finding something other than an opaque rock with a fancy name is not to be taken for granted.
U11138 | “Ruby ID: U11138”
R11625 | “Ruby ID: R11625”
R12260 | “Ruby ID: R12260”
Cut is the third C and the last measurement of quality. Cut is limited by the stuff included in the crystal, and which direction the ruby shows its best colors colors . Due to numerous and ever-present limitations, cutters almost always compromise the cut. Cut is also not as critical for rubies as it is in something like diamonds, where many aspects of their brilliance is derived from this factor. Smaller rubies typically receive better cuts.
R10007 | “Ruby ID: R10007”
R10030 | “Ruby ID: R10030”
R11770 | “Ruby ID: R11770”
The final C is carat weight, and is specifically used as a gauge for overall rarity and the final price. Rubies do not like to grow very large either, with the largest faceted example known being the 32 carat Hope Ruby . It also does not hold a candle to the best quality, large ruby known in existence; the 25 carat Sunrise Ruby . The Sunrise Ruby sold for over 4 times the amount the Hope Ruby did, with better clarity and color. Who knows what the price would have been if the Sunrise was any larger!
A fine example like the Sunrise Ruby is the rarest ruby known. Something of its quality is a one-in-a-lifetime find, as it was for Sotheby’s fine jewelry auctioneer who had 40+ years of industry experience at the time of the auction. It is the current record holder for most expensive ruby ever sold, and most expensive colored gemstone ever sold. Note that diamonds are considered separate from the colored stones market, with most of the gemstone industry revolving around them.