LABRADORESCENT FELSPAR 431 



original deposits. The stone is frequently cut in Ceylon in rounded forms, but so unskilfully 

 that it usually has to be re-cut in Europe. 



A small amount of material is derived from other sources, all of which are less, 

 important than that last mentioned. In Brazil fine crystals occur in gneiss in the neigh- 

 bourhood of Rio de Janeiro, many of which are suitable for cutting as gems. 



In North America moon-stone is found at various places, but the finest specimens 

 come from Allen's Mica Mine at Amelia Court House in Virginia. These colourless and 

 almost transparent fragments, the largest of which are half an inch across, occur embedded 

 in a coarse-grained granite, from which they are won in the course of mining for mica. 

 Moon-stone from this locality is quite comparable in quality to that from Ceylon. 



Here in North America are to be found, besides adularia, other felspars which exhibit 

 the chatoyancy characteristic of moon-stone, though only to a small extent. The external 

 appearance of some of these differs in no wise from that of the adularia-moon-stone hitherto 

 considered, but this is not true in all cases. The colourless and transyyarent soda-felspar^ 

 known as albite, sometimes exhibits the chatoyant appearance in question, and may then be 

 distinguished as albite-moon-stone. A very beautiful example of this is afforded by the 

 albite of Mineral Hill, near Media, in Delaware County, Pennsylvania, which is sometimes, 

 cut as a gem ; also by that from Macomb in St. Lawrence County, New York, which is, 

 distinguished by the name of peristerite. It occurs with ordinary felspar and is sometimes 

 cut as a gem. Many of the crystals of peristerite are chatoyant, and some of these are as. 

 fine as moon-stone from Ceylon ; others are coloured with pale shades of green or yellow, 

 and some specimens show different colours at the same time. Adularescent albite, which, as 

 mentioned above, is distinguished by the name of peristerite, is found in crystals and in 

 large massive pieces in veins of coarse-grained granite penetrating gneiss at Bathurst,, 

 near Perth, and at various other places in Canada. 



Much rarer than moon-stones are transparent felspars with a reddish adularescence and 

 a yellowish colour. They are sometimes referred to as sun-stone, but are quite distinct from 

 the stone of this name described above. They occur at the same localities as moon-stone. 



Very good imitations of moon-stone, which are frequently used in cheap jewellery, have- 

 recently been made in glass, and it is by no means easy to distinguish them by mere 

 inspection from genuine stones. Glass imitations are, however, always denser and less hard 

 than real stones; moreover, moon- stone is distinctly doubly refracting, while the glass, 

 imitations are singly refracting, so that these characters serve to distinguish the two. 



LABRADORESCENT FELSPAR. 



A beautiful coloured sheen is a noticeable feature of the potash-felspar or orthoclase 

 found in the south of Norway between the Christiania and Langesund fjords. It occurs in 

 masses in an augite-syenite, a rock which has sometimes been referred to as zircon-syenite, 

 and is especially abundant in the veins of coarser-grained material by which the rock is. 

 penetrated. As more definite localities, Laurvik and Fredriksvarn, especially the latter,, 

 are often mentioned. The surface which shows the coloured sheen has a rather greasy 

 lustre, and has the same orientation in the crystal as that of the chatoyant surface of a 

 crystal of moon-stone. Contrasted with moon-stone, however, this felspar is grey and 

 opaque, and its sheen, instead of being of a milky blue tinge, is of a very fine blue colour, 

 or in rare cases green, yellow, or red. The sheen is also much more intense and brilliant 

 than in moon-stone, and thus approaches more nearly to that of labradorite without ever 



