Indicolite is a mineral with a hardness of 8 out of 10 on the Mohs scale of mineral hardness [?]. These Trigonally structured gems are made of complex borosilicate, their full chemical compound being Na(Li,al)3Al6(BO3)3Si6O18(OH)4.
Indicolite is the blue sodium-rich variety of Tourmaline, and may come in all shades of blue, from light-blue, violet-blue to deep red or deep green.
It generally appears quite a deep blue, even the color of dark blue ink, perhaps appearing green in one direction because of its strong pleochroism. Sometimes indicolite is an overall greenish blue, which, unlike the color of greenish blue sapphire, is very attractive.
Its greenish blue color is unmistakable and particularly attractive. Loss of transparency in one direction is another distinctive characteristic and is best seen in rectangular gems. Because of its appreciable birefringence, if the stone is examined with a standard jeweler's 10x lens, the opposite facet edges look double in certain directions.
Stones are often clear and free of inclusions, but intense pleochroism may make them so dark in one direction as to appear lacking in transparency.
Indicolite Tourmaline is mainly found in Minas Gerais (Brazil), Colorado, Massachusetts, California (USA, Namibia, Madagascar, and the Ural mountains (Russia).
It is also known as blue tourmaline.
It is mistakenly called indigolite or Brazilian sapphire.
Indicolite derives its name from the indigo color.
This gem is given mixed, faceted, and also rectangular, step cuts, as it has good luster. Attractive, definite blue or blue-green stones are priced similarly to fine rubellites, and are less common. But when the color is too deep, and inky blue, the value falls considerably, as it does with the less attractive rubellites. It is neither imitated nor produced synthetically.