Sugilite

The mineral sugilite was first described in 1976 by Murakami and his co-workers in the Mineralogical Journal of Japan, and was named in honour of the late Professor Kan-ichi Sugi. As first discovered the mineral consisted of brownish-yellow grains in an aegirine syenite from Iwagi Islet, Ehemi Prefecture, Japan. The mineral is hexagonal in structure, with hardness 6 on Mohs' scale, density 2.74 and refractive indices 1.607 for the extraordinary and 1.610 for the ordinary ray. In composition, sugilite is a complex silicate of alkali metals, iron, aluminium, etc. and contains water. In its composition, crystal structure and physical properties it closely resembles another rare mineral sogdianite (first described in 1968) with which it has in fact been confused. Sogdianite, however, contains essential zirconium and has a rather higher density (2.82-2.90).

The yellow-brown grains of sugilite as originally discovered had nothing to offer as a gem material, but more recently a very different and strikingly handsome manganoan form of the mineral has been recovered from the Wessel Mine, Hotazel, in the North Province of South Africa. Here the mineral is found in the form of a purple rock-like material of which 'Royal Azel' and 'Royal Lavulite' have proved the most popular. As an aid to the gemmologist in the identification of this manganoan form of sugilite by standard techniques the presence of three fairly sharp bands in the violet region at 4110, 4190 and 4370, due to manganese, should be mentioned. These bands were first recorded by R Dillman, and being at the violet end of the spectrum can. only successfully be observed by using a powerful beam of light which has passed through a good blue filter.

from "Gems, Their Sources, Descriptions and Identification," by Robert Webster and BW Anderson, 1962. Copyright © 1983.