This blue gemstone is also known as iolite, dichroite, "water sapphire", "lynx sapphire", and "bloodshot iolite". The Greek word "io", meaning the violet flower, is the source of the name most used. Its distinct pleochroism explains the name dichroite. In Sri Lanka, the lighter colored tumbled pebbles were known as "water sapphires". The term "lynx sapphire" denoted the darker indigo blue stones.
Orientation of the table in faceted stones greatly affects the perceived color of the finished gem. Usually, the optimum color is achieved by placement of this facet perpendicular to the direction where the most intense blue is observed. In volume two of "Precious Stones", Dr. Max Bauer describes a cut that exhibits the distinct pleochroism of iolite. "This object is attained by cutting a cube, the faces of which are perpendicular to the three axes of the crystal. The cube is mounted by one corner on a pivot, so as to show the three different colored faces, and forms an interesting and remarkable object." Some iolites cut en cabochon display opalescense resembling star sapphires. An excellent picture of the hematite platelet inclusions in "bloodshot iolite" appears on page 164 in the "Photoatlas of Inclusions in Gemstones" by E.J. Gubelin and J.I. Koivula.
The ferrous oxide content of cordierite influences its color and causes considerable variation in the specific gravity. With the density, hardness, and double refraction indices so similar to those of quartz, cordierite can easily be confused with quartz. However, these same properties help to distinguish it from other blue gemstones. Praseolite is the unusual leek-green colored cordierite. It is both ironic and confusing that some amethyst from Brazil and Arizona changed by heat treatment to a very similar leek-green color is called Praseolite. Distinguishing between the two could depend on optically locating the interference figures or a more sophisticated analysis. Praseolite (cordierite) is biaxial. Praseolite (green quartz) is uniaxial.
Stubby prismatic gemmy crystals and pebbles occur in the gem gravels of Sri Lanka, Burma, and Madras in India. The especially fine material now comes from Madagascar. Other sources include: Karasburg in Namibia, Babati in Tanzania, Bavaria, Orijarvi in Finland, and the area around Murzinka in the Ural mountains. Gems up to two carats can be cut from some crystals found in Haddam and Guilford, Connecticut. Gemmy nodules occur in Virgolandia and Paraiba of Brazil. Granules are found in regions of metamorphosed pelitic (clay) rock, some igneous rocks, and pegmatites throughout the world. Kragero in Norway and Sri Lanka are sites of vitreous massive material containing the red hematite platelets.
Despite its popularity in Europe during the eighteenth century, iolite is not so well known by the public today. Its pleochroism is especially suited to a brilliant lenticular cut and to a fairly shallow step-cut. Iolite is somewhat brittle, but with its satisfactory toughness and a hardness exceeding that of quartz, it adds a sapphire-hue choice to the array of the less expensive, but more durable stones suitable for rings as well as other jewelry.