Teal Sapphire

Teal sapphire is a very difficult product to produce consistently. The color teal is produced by cobalt.  Depending on the atmosphere, temperature, etc the sapphire crystals can differ drastically from one to another. Cobalt takes on two valence charges in sapphire Co3+ (Green) and Co2+ (Blue). We have yet to see teal colored czochralski sapphire, but there are patchy green / blue flame fusion sapphire products that can be trimmed to cut a teal colored gem. Green sapphire is a relatively rare product compared to many other colors of sapphire, and because teal is usually caused as a uncontrollable byproduct of green sapphire production, that makes teal sapphire even more rare. The neat thing about teal sapphire is that no two gems have exactly the same color due to the random mixing of Co3+ and Co2+. 

A consistent vivid teal "paraiba" colored sapphire is one of the holy grails of lab sapphires that will hopefully be produced one day soon.