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History & Introduction

Iolite gemstone is a transparent gem-quality form of cordierite, a composition of magnesium iron aluminum cyclosilicate mineral. Even though the mineral has history of dates back hundreds of years, the actual gemstone 'iolite' is considerably relatively new and little known. The first significant and exciting discovery of large iolite gem in transparent, gem-quality was made in 1996 in Palmer Creek, Wisconsin (USA) by W. Dan Hausal, an American geologist. The largest iolite crystal in the world was discovered south of Palmer Creek, in Grizzly Creek, Wisconsin and its weight is above 24,000 carats.

The name 'iolite' comes from the Greek word 'ios' that means 'violet'. Iolite's strong pleochroism received the misleading trade name of 'water-sapphire', a name now obsolete. The view of the gemstone is as from one direction, appears sapphire-like blue and from another appears as clean like water. Furthermore, from the top view down, it appears light golden or honey-yellow in color. 'Dichroite' is another word for iolite in reference to its pleochroic ability; 'dichroite' is a Greek word that loosely means as 'two-colored rock'. Iolite gemstone is even famous for 'the Viking stone' because according to Norse legend, Vikings used iolite as a polarizing filter to help them find the sun on cloudy days.

Recognise - Gem-quality of iolite gemstone varies in color that is from sapphire blue to violet-like blue and from light-blue to yellowish-gray. The strong pleochroic characteristics is often used to identify and discern the gemstone amongst other similar colored gemstones. At times iolite is mistaken for sapphire and tanzanite, however it is softer as compared to sapphire, but harder than tanzanite. Other gems that may even cause confusion that includes spinel and garnet, however both spinel and garnet are refractive in a single manner that means the iolite's trichroism is absent.

Availability - The deposits of iolite gemstone is found in numerous locations around the world. Maximum iolite gemstones come from India, however there are other significant sources too like Myanmar (Burma), Australia (Northern Territory), Canada (Yellowknife), Brazil, Madagascar, Namibia, Sri Lanka (Ceylon), Tanzania and the United States including Wyoming and Connecticut.

Buying Guide

Color - Naturally the iolite stone is in light to dark blue and violet, though it is even available in various shades of green, yellow, brown or gray. The maximum color in demand is an intense violet blue, which is the rival of tanzanite. Iolite is trichroic that deals with three different colors, which is seen in the same stone depending on the viewing angle. Few of the less grade or poorly cut iolite appears overly dark or 'inky', gives a closer look to blackish.

Clarity and Lustre - The mineral cordierite is looks naturally opaque, but fine gem-quality iolite looks like transparent to translucent in terms of clarity. In many cases, the cutting quality of the gem affects the clarity. Stones when are cut too deep appears to be opaque. Mainly the iolite shows few of the visible inclusions, especially in larger stones. Though they are rarely seen, eye-clean specimens are not unheard of. After it is polished, iolite displays an oily to vitreous luster.

Cut and Shape - This gemstone is quite often step cut to enhance color and to lighten the tone it is regularly intentionally 'windowed' or shallow cut. Cutters must properly angle the rough seeing the iolite's trichroism of blue, gray and near colorless forms. Mainly the common shapes for finished stones adds up to traditional faceted rounds, pear and ovals shapes. Fancy shapes and calibrated sizes are relatively accessible.

Treatment - For the case of iolite known treatments or enhancements are there, though there is the availability of synthetic cordierite that is primarily used for ceramics and other industrial purposes.

Gemological Characteristics:

Chemical Formula Mg2Al3[AlSi5O18] Magnesium aluminum silicate
Crystal Structure Orthorhombic; short prisms
Color Blue, brownish, yellowish, gray, violet
Hardness From 7 to 7.5
Refractive Index From 1.542 to 1.578
Density From 2.58 to 2.66
Cleavage Good
Transparency Transparent, translucent
Double Refraction or Birefringence From -0.008 to -0.012
Lustre Vitreous
Fluorescence Not there


  • Blue iolite