4-28 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



It follows the vertical banding of the gneiss, which in the immediate neighbourhood passes- 

 into a mica-schist very rich in mica, or possibly into pure mica. Accompanying the 

 sun-stone in this vein are a variety of minerals, including haematite, cordierite, hornblende,, 

 zircon, and probably also apatite. The felspar found near the margins of the vein is 

 almost colourless, and does not show the metallic sheen characteristic of sun-stone. That 

 found nearer the centre of the vein encloses more scales of haematite, and at the same time 

 exhibits a marked metallic sheen. The finest material is usually obtained from the centre- 

 of the vein ; it occurs in irregular masses embedded in stuff of inferior quality which has to 

 be cut away, the better portions only being kept for use. 



Sun-stone occurs also in North America, for example, at Statesville in North 

 Carolina. Some of the material found there is equal to Norwegian sun-stone, although the- 

 enclosed scales of haematite are much smaller than those enclosed in material from the latter 

 locality. It is found at Fairfield in Pennsylvania and at other places in the same State. 

 At Middletown, in Delaware County, Pennsylvania, very fine material, little inferior tO' 

 Norwegian sun-stone, is found, with moon-stone, loose on the surface of the ground. At 

 Media in the same county there is found, besides the brilliant red sun-stone, a variety 

 of felspar which shows the same kind of sheen as sun-stone, but which is green instead of 

 red in colour. 



The sun-stone found at all the above-mentioned localities may be described as a triclinic 

 lime-soda-felspar, in which the soda preponderates over the lime ; it is known mineralogically 

 as oligoclase. The avanturine-felspar, so far considered, is thus a variety of the mineral 

 species oligoclase, which is distinguished from ordinary oligoclase by the possession of a. 

 metallic sheen due to the enclosure of scales of haematite. Like all triclinic felspars, the 

 sun-stone variety of oligoclase, or oUgoclase-suv^stane, shows a series of fine striations on 

 the principal cleavage face, that is to say, on the face which exhibits the metallic sheen. 

 These striations have the appearance of straight lines running parallel to the plane of the 

 less perfect cleavage, that is to say, parallel to the intersection of the two cleavage surfaces. 

 TTiey are a result of the peculiar repeated twinning of the crystal, and are not present in 

 the avanturine-felspar to be presently considered. This difference, therefore, serves to. 

 distinguish the two kinds of avanturine-felspar when in the rough, but on cut and polished 

 stones the striations are not seen. 



The appearances characteristic ot sun-stone are not limited entirely to oligoclase,. 

 but are exhibited also by other kinds of felspar, especially by certain specimens of potash- 

 felspar or orthoclase. In these stones are enclosed thin scales of hasmatite, arranged 

 parallel to the plane of perfect cleavage, which produce a glittering metallic sheen precisely 

 similar to that of sun-stone already described. This orthoclase-mn-stone is found principally 

 in North America, for example, at Glen Riddle, in Delaware County, Pennsylvania, where 

 the felspar is salmon-coloured and partly transparent. Beautiful varieties of orthoclase- 

 sun-stone have been discovered near Crown Point, in the State of New York. On the 

 Horace Greeley farm at Chappaqua, New York, have been found small pieces of the same 

 stone, almost equal to that found at Tvedestrand, Norway ; while in Virginia specimens have 

 been met with at Amelia Cpurt House in Amelia County. 



Sun-stone is in every case cut with a quite flat or slightly convex surface parallel to the- 

 face showing the sheen. The stone is by no means extensively used, and moderately high 

 prices are paid only for the finest specimens. 



Avanturine-felspar can be readily distinguished even with the naked eye from avan- 

 turine proper, that is avanturine-quartz, so that these stones are seldom mistaken one- 

 for another. In doubtful cases the hardness forms a distinguishing feature ; for while the 



