Enter the most famous sky blue gemstone traded today; aquamarine. It's a chemical cousin of emerald, belonging to the same gem species known as beryl. The gem's name is a direct reference to the greenish blues of crystal clear ocean water. It's been prized by nations as the second most expensive beryl species used for jewelry in modern times.
Aquamarine (pictured above), though beautiful in its own 'natural-color' state, is often heated to remove any yellowish modifying colors in order to portray a more pure blue body. This is most often undetectable even by many gemological instruments, and is commonly practiced by a vast majority of gem dealers today. Despite this treatment's presence, it does not mean that aquamarine's colors have no hierarchy. The treatment removes yellow colors, but a gem's star-quality potential still has to be present in its original crystal. Some aquamarine specimens will look dull and grayish no matter what degree of heat is applied to it. This fact means the variety's top colors can hold high values due to rarity, demand and exclusivity.
Darker toned aquamarines with higher saturations are much rarer and much more valuable than lighter ones, even with both having been heat treated. The gemstone's finest locality source is the Santa Maria area of Minas Gerais in Brazil, which is famous for producing many of the world's top quality blue beryls.
On the other side of the fence, another popular sky blue gem has been making waves for the past several decades. Blue topaz can come in an entire range of tones and saturations due to advancements in irradiation and annealing treatments. Topaz typically comes out of the ground in warmer or grayish colors, but the most popular trade varieties today are 'London Blue', 'Swiss Blue' and 'Sky Blue', all priced affordably in most countries.
Depicted in the picture above is the 'Ostro Stone' topaz, the biggest of its kind- weighing in at around 9,381 carats. As you can see, due to the industry being able to mine topaz specimens in large sizes, candidates for heating are not in low supply. Add to this the possibility of high-saturation color treatments and you acquire marvels like this specimen.
The difference between aquamarine and topaz (aside from obvious chemistry), is that blue topaz' colors don't have much of a hierarchy. Yes, topaz is a natural gem mined from the earth, but its bluish hue is completely re-creatable even in near-colorless parcels. This is very different from aquamarine's limited supply of high-saturation stones (especially in smaller carat sizes).
The supply of blue topaz has quenched the increasing demand for pastel blue hues, bringing it to be one of the most popular gems for the color palette used today. The question is, who wins? Aquamarine with more rarity and monetary value, or blue topaz with more affordability and diversity of color tone?
