1911 Encyclopædia Britannica/Axinite

by Leonard James Spencer

AXINITE, a mineral consisting of a complex aluminium and calcium boro-silicate with a small amount of basic hydrogen; the calcium is partly replaced in varying amounts by ferrous iron and manganese, and the aluminium by ferric iron: the formula is HCa₃BAl₂(SiO₄)₄. The mineral was named (from ἀξίνη, an axe) by R. J. Haüy in 1799, on account of the characteristic thin wedge-like form of its anorthic crystals. The colour is usually clove-brown, but rarely it has a violet tinge (on this account the mineral was named yanolite, meaning violet stone, by J. C. Delamétherie in 1792). The best specimens are afforded by the beautifully developed transparent glassy crystals, found with albite, prehnite and quartz, in a zone of amphibolite and chlorite-schists at Le Bourg d’Oisans in Dauphiné. It is found in the greenstone and hornblende-schists of Batallack Head near St Just in Cornwall, and in diabase in the Harz; and small ones in Maine and in Northampton county, Pennsylvania, U.S.A. Large crystals have also been found in Japan. In its occurrence in basic rather than in acid eruptive rocks, axinite differs from the boro-silicate tourmaline, which is usually found in granite. The specific gravity is 3·28. The hardness of 61/2–7, combined with the colour and transparency, renders axinite applicable for use as a gemstone, the Dauphiné crystals being occasionally cut for this purpose.  (L. J. S.)