THE FELSPAR GROUP (SUN-STONE) 427 



iron) arranged parallel to the direction of perfect cleavage in the felspar. The glittering 

 reflection is therefore confined to the cleavage siirfaces ; other faces, parallel to which there 

 •are no inclusions, do not show it. The enclosed scales of haematite have a regular six-sided 

 or rhomb-shaped outline, or they may be quite irregular. These scales, in consequence of 

 their excessive tenuity, are transparent ; they have a red colour, which may be distinctly seen 

 when thin sections of the stone, cut parallel to the plane of reflection, are examined under 

 the microscope. It is to the reflection of brilliant red metallic light from the surface of 

 these scales that the glittering sheen of the stone is due. The more numerous and 

 regularly distributed are these scales the more brilliant and uninterrupted is the reflection 

 from the surface of the stone. If they are altogether absent there is no trace of the peculiar 

 appearance characteristic of sun-stone ; moreover, when the stone is turned about so that 

 the reflecting surface is inclined towards the light at different angles the metallic sheen 

 will be observed to appear and disappear. The metallic reflection is, of course, dull or 

 -absent in those portions of the stone in which the enclosures of hasmatite are few in 

 number or altogether lacking, and in working the stone such parts are cut away and 

 ■discarded. Sun-stone is very similar in appearance to that variety of quartz which is 

 known as avanturine, and for this reason is sometimes referred to as avanturine- 

 felspar. 



At the beginning of the nineteenth century sun-stone was a great rarity and very 

 ■costly. There were only a few small pieces known to be in existence, and the single locality 

 .given for it was Sattel Island (Setlovatoi Ostrov) in the White Sea near Archangel. The 

 fragments of sun-stone found here were described as masses of cloudy, white, translucent 

 felspar, in which were portions here and there showing a golden sheen. Subsequently the 

 East Indies and Ceylon were mentioned as localities for sun-stone, but the occurrence of the 

 -stone there is probably not authentic. 



In the year 1831 an occurrence of sun-stone was discovered at Verchne Udinsk on the 

 Selenga, a river flowing into Lake Baikal in Siberia. The sun-stone is found here in a 

 narrow vein of felspar, which runs vertically through a black rock. It is of a clove-brown 

 colour, and in this case also the sheen is due to the enclosure of scales of haematite, which 



• are arranged parallel to the plane of easier cleavage. The scales are present in large 

 numbers, and when the cleavage face is inclined towards the light at a suitable angle a 

 multitude of shining golden scales become visible. In all other positions the stone appears 

 iustreless and of a uniform brown colour, but when turned in this one direction it appears 

 as if suddenly gilded, producing a surprisingly beautiful effect. Even from broken frag- 

 ments lying on the surface of the ground, and exposed to the action of weathering agencies, 

 material was obtained superior to any which had been previously found. From a vein of 



• considerable thickness below the surface were found bigger and more compact masses large 

 enough to be worked into objects of some size, such as bowls and vases. Sun-stone also 



• occurs as rounded pebbles in the Selenga river; these had been occasionally collected 

 ■by passing merchants some time before the mineral was discovered in its original 

 situation. 



The most typical and beautiful sun-stone was discovered in the 'fifties at Tvedestrand 

 in the south of Norway, where it occurs in situ. It is also found imder similar conditions 

 -at Hittero on the Christiania fjord. The sun-stone from the same region, for which 

 Fredriksvarn was previously given as the locality, probably came in reality from Tvedestrand. 

 The mineral never occurs in this region in regularly developed crystals, but always in 

 masses embedded in white quartz, which forms a vein penetrating gneiss. This vein has on 

 .an average a thickness of a yard and has been worked for a length of at least six yards. 



