Iolite
Iolite (gemology) is a relatively modern gemstone that displays a beautiful blue-violet color. Discovered during the 19th century in Spain, one of its names was derived from the Greek word ιωδες for violet, while its other name was taken from the geologist Louis Cordier (1777-1861). Cordierite (mineralogy) is a silicate infused with aluminum, iron, and magnesium. Cordierite can be associated with spinel and kyanite in metamorphic rock. How the mineral cordierite came to be identified as the crystal is a bit of a mystery to me because the difference between mineral and gem qualities are large. The International Colored Gemstone Association says, iolite was used by the Vikings as a navigation tool and mined by them in Norway, yet research has shown this tool to be made of sunstone. On a less critical note, iolite is one of a few gemstones that cannot undergo heat treatment, the equivalent of color-fastening; so, the iolite crystal once faceted and polished will not color-unfasten. When exposed to the weather, however, it can even alter in composition. You may run across fading with irradiated crystals. Over time, synthetic cordierite has replaced iolite for its industrial uses like many other mined minerals. While this gem can be produced in a laboratory, the mined variety has the benefit of natural pleochroism. Only transparent, gem-quality cordierite is known as “iolite”; moreover, its older name, dichroite, referred to cordierite’s pleochroism. The past name just seems vague. When this gemstone was viewed at on its axis, its color was similar to a sapphire — some other direction, it would appear as clear. From this, another name for the iolite gem was “water-sapphire”. An example of the phenomenon is the rotation of the raw crystal by 90 degrees from the maximum violet color. The axis of maximum color must be perpendicular to the table after faceting, however. Jewelers have utilized the blue-violet color of this gemstone since it can closely resemble tanzanite, another gem that does not receive heat or irradiation treatments. The price for this gemstone is affordable, because iolite has failed in mass-markets, is known to be vulnerable to cleavage, and can break when worn as a ring.
Pierre Louis Antoine Cordier (1777-1861) was a French geologist, mineralogist, and professor of geology. He worked at the Museum National d'Histoire Naturelle in Paris from 1819 until his death 1861. His courses in geology included an expedition to the Alps and Napoleon's expedition to Egypt. After researching the Nile valley, he and his instructor, Deodat Gratet de Dolomieu, were taken prisoner in Taranto before returning to France three months later. Appointed director of the Museum, his collection included thousands of specimens sent from colleagues over the globe; moreover, he classified 337 rock types by 1844. The mineral Cordierite was given his name in commemoration.