Iolite
Iolite is a blue silicate mineral that occurs as clear crystals and used as a gemstone. Mineralogists call this mineral cordierite and it is also sometimes called dichroite (it is actually trichroic) because of its marked pleochroism.
Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles or in different direction, especially with polarized light. Iolite is strongly pleochroic and hence shows different colors when viewed in different directions. A cube cut from iolite will look a more or less violet blue, almost like sapphire, from one side, clear as water from the other, and a honey yellow from on top. In the past, this property led some people to call iolite ‘water sapphire’, though the name is now obsolete and showed not to be used.
History of gemstone iolite: A legend of iolite has it that when Viking sailors ventured off the coast into the Atlantic Ocean they used a gem compass to help determine their position. This gemstone compass was made from natural iolite. By using thin pieces of gem quality iolite and looking through it, navigators could determine the exact position of the sun and thereby navigate their way safely to the New World and back.
Iolite is named the mineral cordierite after the French geologist P.L.A. Cordier. Cordierite was discovered in 1813. The term iolite comes from the Greek word ‘ion’. In the Greek language, Ion refers to the color violet or purplish blue color.
The chemical composition of iolite is magnesium aluminium silicate (Mg2 Al4Si5O18). Iolite crystallizes in the orthorhombic system often as short prisms. The specific gravity ranges from 2.57 to 2.66 and the refractive index range vary between 1.53-1.54 and 1.54-1.55 and a birefringence from 0.008 to 0.012. Iolite’s hardness on Mohs scale ranges between 7 and 7.5. Typical stones are available from 1-10 carats with fine quality iolite gems above 5 carat are very rare.
Since iolite is strongly pleochroic, it is very important that the gem stone rough be cut and faceted using the proper directions to show off the best blue color. If the gem is cut properly, the stone shows a deep blue color through the top and appears colorless if viewed from another angle. A common adage for iolite is the richer the blue, the better the color. If iolite is not cut with the right direction, no matter what the shape of the raw crystal, its color will not be displayed to its best advantage. Iolite gem stone is mainly transparent or translucent stone.
Gem quality iolite varies in color from sapphire blue to blue violet to yellowish gray to light blue as the light angle changes. Iolite is abundantly found in Australia (Northern Territory), Brazil, Burma, Canada (Yellowknife area of the Northwest Territories), India, Madagascar, Namibia, Sri Lanka, Tanzania and the United States (Connecticut). The largest iolite crystal found weighed more than 24,000 carats, and was discovered in Wyoming, US. It often occurs in the gem gravels of Sri Lanka. As an uncommon gemstone, iolite is not treated or synthetically produced.
While one could use blue sapphire, amethyst, scapolite or tanzanite as a gemstone that resembles iolite, the fact is that the iolite is more easily used as a simulant of the blue sapphire.
For those that believe in the power of gemstone lore, iolite is believed to awaken the third eye, stimulate visions and connect one with one’s own inner wisdom. It is said that it helps individuals live in the present as well.
Gem quality iolite varies in color from sapphire blue to blue violet to yellowish gray to light blue as the light angle changes. Iolite is sometimes used as an inexpensive substitute for sapphire. It is much softer than sapphires and is abundantly found in Australia (Northern Territory), Brazil, Burma, Canada (Yellowknife area of the Northwest Territories), India, Madagascar, Namibia, Sri Lanka, Tanzania and the United States. The largest iolite crystal found weighed more than 24,000 carats, and was discovered in Wyoming, US.
