When pricing sapphires, medium blues are usually the most expensive.Ĭorundum can show a phenomenon called asterism, or the star effect.
The very finest sapphires are a velvet, slightly violetish medium to medium dark blue, often called Kashmir blue, after its original location in India. Sapphire comes in a wide range of blues, varying from very light blue to a deep blue that is almost black. Chromium causes the red color of rubies and the pink of pink sapphire. Only a few hundredths of a percent of iron and titanium can cause the color, and the more iron the corundum contains, the darker the blue. When the trace elements are iron and titanium, the corundum is blue sapphire. Most corundum contains color-causing trace elements.
Colorless sapphires were once popular diamond imitations, and they’ve staged a comeback as accent stones in recent years.īut colorless corundum is rare. In its purest state, corundum is actually colorless. However, silicon is a very common element, making natural corundum relatively uncommon. The mineral corundum is composed only of aluminum and oxygen, and it requires a growth environment that’s free of silicon. Sapphires belong to the mineral species corundum, and also apply to any corundum that is not red or doesn’t qualify as red.
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