THE PYROXENE AND AMPHIBOLE GROUPS (SPODUMENE) 455 



SPODUMENE. 



Spodumene is a member of the pyroxene group which usually occurs as opaque, ash- 

 grey crystals ; only rarely is it transparent and suitable for gem purposes. A beautiful 

 green, transparent variety is known as hiddenite. Chemically, spodumene is a silicate of 

 lithium and aluminium with the formula LigO.AlgOg.^SiOj ; other elements, including iron, 

 are also present, but only in small amount. From the fact that lithia is an essential 

 constituent of hiddenite, this emerald-green variety of spodumene is sometimes referred to 

 as "lithia-emeraid." It resembles the emerald, however, only in the green colour, which is 

 probably due to the presence of a small amount of iron or chromium. 



Spodumene occurs in monoelinic crystals of prismatic habit and vitreous lustre. These 

 crystals possess a very perfect cleavage parallel to the faces of the prism. In the transparent 

 varieties the colour is usually pale yellow or yellowish-green, but some crystals (of the 

 hiddenite variety) have an emerald-green tint which, however, is never as deep and pure as 

 that of the finest emeralds. The two stones differ in that while spodumene is rather 

 strongly dichroic, emerald is only feebly so. 



Spodumene has a specific gravitv of 3"17, and this is another feature which distinguishes 

 the stone from emerald, for the specific gravity of the latter does not exceed 2"7. Moreover, 

 the hardness of spodumene varies between 6^ and 7, while in the case of emerald 

 H = 7'^ to 8. Hence the former mineral is, and the latter is not, scratched by quartz, and, 

 conversely, while emerald is capable of scratching quartz spodumene is not. 



Spodumene of gem-quality is exclusively an American product, having been found only 

 at one locality in the United States, namely, at Stony Point, Alexandra County, North 

 Carolina, and in Brazil. 



In North. Carolina the hiddenite variety is found at Stony Point, the name of which 

 place has been altered to Hiddenite, associated with emerald, beryl, quartz, garnet, rutile, 

 and other minerals, in drusy cavities in a gneissose granite. The first specimens of hiddenite 

 were discovered in 1879 by Mr. W. E. Hidden; they had been weathered out of the 

 mother-rock and were lying loosely in the ground. They were transparent and greenish- 

 yellow in colour and were at first thought to be diopside, since at that time spodumene had 

 never been found in fine, transparent crystals. A closer examination revealed their true 

 nature, and later on, during systematic mining operations for emerald in the same locality, 

 crystals of hiddenite were found in the original mother-rock. The size of the crystals varies 

 considerably, the largest prisms having a length of 7 centimetres. Some crystals are 

 remarkable for the possession of a peculiar corroded surface. Some, again, were of an 

 «merald-green colour ; these and the more ordinary yellowish-green crystals were all cut as 

 gems. Very few of these cut stones have found their way into Europe, the majority having 

 been kept in the country as objects of local interest ; a fine cut stone is, however, to be seen 

 in the Mineral Collection of the British Museum (Natural History). Fine, green, transparent 

 hiddenite is worth from 50 to 100 dollai's ^10 to £20) per carat, and the mineral is more 

 likely to rise than to fall in value, since the deposit at Stony Point appears to be completely 

 exhausted and no other has as yet been discovered. Altogether about 7000 dollars' worth 

 of rough material has been obtained from this one deposit. 



More recently fine, transparent specimens of spodumene of a pale yellow, rather than a 

 green colour, have found their way from Brazil into the European markets under the 

 name of chrysoberyl. This yello^^', transparent spodumene occurs in Brazil in association 



