Gem quality cordierite has the same name(or rather name) as the mineral, but was in the past also known as water sapphire, particularly when the color was not very intense. This is perhaps most familiar name in the trade.



Appearance:
The color may vary from a quite a deep blue to violet blue, light blue or grayish blue; but it always has very strong pleochroism, being a much lighter grey or wan yellow in one direction. For oblivious, aesthetic reasons, gems are cut so that this color is only visible from the side. The most common cut is rectangular, step cut, not always truncated corners. One also comes across cordierite with a cabochon cut or minutely in engraved particularly in the case of less transparent specimens with numerous inclusions. Most stones are few carat in weight; not too small, therefore, but never very large.



Distinct feature:
An essential characteristic of cordierite is its exceptional pleochroism, which may, however, resemble certain Tanzanite’s. Many cordierites have a decidedly cold, grayish coloration, whereas tanzanite is a warmer color, always with a hint of violet. Testing the density, which is very different, would remove any uncertainty.



Occurrence:
Cordierite comes mainly from the gem gravels of Sri Lanka, but also from the United States, Namibia.



Value:
Rather low, that of minor gemstone.