IOLITE, a mineral occasionally cut as a gem-stone, and named from the violet colour which it sometimes presents (ἴον, “violet”; λίθος, “stone”). It is generally called by petrographers cordierite, a name given by R. J. Haüy in honour of the French mineralogist, P. L. Cordier, who discovered its remarkable dichroism, and suggested for it the name dichroite, still sometimes used. The difference of colour which it shows in different directions is so marked as to be well seen without the dichroscope. The typical colours are deep blue, pale blue and yellowish grey. While the crystal as a whole shows these three colours, each face is dichroic.
Iolite is a hydrous magnesium and aluminium silicate, with ferrous iron partially replacing magnesium. It crystallizes in the orthorhombic system. In hardness and specific gravity it much resembles quartz. The transparent blue or violet variety used as a gem occurs as pebbles in the gravels of Ceylon, and bears in many cases a resemblance to sapphire. The paler kinds are often called water-sapphire (saphir d’eau of French jewellers) and the darker kinds lynx-sapphire; the shade of colour varying with the direction in which the stone is cut. From sapphire the iolite is readily distinguished by its stronger pleochroism, its lower density (about 2.6) and its inferior hardness (about 7).
Iolite occurs in granite and in true eruptive rocks, but is most characteristically developed as a product of contact metamorphism in gneiss and altered slates. A variety occurring at the contact of clay-slate and granite on the border of the provinces of Shimotsuké and Ködzuké in Japan has been called cerasite. It readily suffers chemical change, and gives rise to a number of alteration-products, of which pinite is a characteristic example.
Although iolite, or cordierite, is rather widely distributed as a constituent of certain rocks, fine crystals of the mineral are of very limited occurrence. One of the best-known localities is Bodenmais, in Bavaria, where it occurs with pyrrhotite in a granite matrix. It is found also in Norway, Sweden and Finland, in Saxony and in Switzerland. Large crystals are developed in veins of granite running through gneiss at Haddam, Connecticut; and it is known at many other localities in the United States.
(F. W. R.*)
ION, of Chios, Greek poet, lived in the age of Pericles. At an early age he went to Athens, where he made the acquaintance of Aeschylus. He was a great admirer of Cimon and an opponent of Pericles. He subsequently met Sophocles in his native island at the time of the Samian war. From Aristophanes (Peace, 830 ff.) it is concluded that he died before the production of that play (421). His first tragedy was produced between 452-449 B.C.; and he was third to Euripides and Iophon in the tragic contest of 429. In a subsequent year he gained both the tragic and dithyrambic prizes, and in honour of his victory gave a jar of Chian wine to every Athenian citizen (Athenaeus p. 3). He is further credited by the scholiast on Aristophanes (loc. cit.) with having composed comedies, dithyrambs, epigrams, paeans, hymns, scolia, encomia and elegies; and he is the reputed author of a philosophical treatise on the mystic number three. His historical or biographical works were five in number, and included an account of the antiquities of Chios and of ἐπιδημίαι, recollections of visitors to the island.
See C. Nieberding, De Ionis Chii vita (1836, containing the fragments); F. Allègre, De Ione Chio (1890), an exhaustive monograph; and Bentley, Epistola ad Millium.