Professor Duns on an ^tndescrihed variety of Amethyst. 349 



scarcely to call for remark. There is still some difference of 

 opinion as to its constituents, traceable no doubt to the fact, 

 that these are not constant, but vary in different specimens. 

 Rose's analysis, which is that most generally received, is as 

 follows : silica 97*50, alumina 0-75, iron oxide and traces 

 of manganese 0*75. In a BraziKan specimen, Heintz (quoted 

 by Dana) found traces of magnesia and soda, whose presence 

 he thinks accounts for the characteristic colour of this 

 mineral. Others hold this to be due to a small percentage of 

 oxide of manganese. Amethyst occurs in veins, or lining the 

 oft-described agate balls. "Crystals within the geodes or 

 hollow agate balls are very often of an amethyst colour, 

 and some are very fine" (Cronstedt's "Mineralogy," vol. i., p. 

 151, 1788). I am able to show to the Society, a very beautiful 

 group of pure amethyst crystals in an agate ball from 

 Saxony. The gem known as oriental amethyst is spinel or 

 dodecctJieclral corundum, a widely different mineral with an 

 amethystine hue. The constituents of spinel are alumina 

 74*50, silica 15-56, magnesia 8*25, oxide of iron 1*56, lime 

 0-75. 



The variety of amethyst which forms the subject of this 

 notice was presented to me, without any reference whatever 

 to its scientific interest, but simply as an ornamental stone, 

 by the Rev. Dr Paterson, New Glasgow, Nova Scotia, who had 

 obtained it at Prince Arthur's Landing, on the north shore of 

 Lake Superior, in August 1878. Looking at it with a good 

 lens I remarked to Dr Paterson, the specimen is altogether 

 unlike any I have seen. The dark red crystalline substance 

 on the faces of the hexagonal pyramids is not deposited in a 

 homogeneous layer, but seems to consist of innumerable 

 spots, I should say of iron oxide. As the donor thought it 

 must have been described, I consulted most of the leading 

 authorities, without, however, finding any reference to this 

 variety. In a note dated August 2, 1879, Dr Paterson says, 

 "I find that the amethyst from Lake Superior has been 

 analysed by Sterry Hunt of the Canadian Geological Survey, 

 who discovered the colouring matter to be oxide of iron 

 before you'' On being asked for a reference, he informed me 

 in a subsequent note, that having failed to find it, he had 



