TOPAZ: OCCURRENCE IN SAXONY 333 



•and hence can be purchased at very moderate prices. This applies more particularly to the 

 ■common yellow topaz ; the red, dark brownish-yellow, colourless, and fine blue varieties 

 •command somewhat higher prices. The finest topaz is, at the present time, not worth more 

 than 10s. per carat, while much less will be paid for inferior qualities. About thirty-five 

 years ago topaz had quite three times its present value ; thus, for a water-clear or rose-topaz 

 weighing 1 carat about 30s. would be paid, for a burnt topaz about 18s., and for ordinar}- 

 yellow 12s. The wholesale price of uncut yellow topaz is now from Is. to 20s. per pound. 



The faults, the presence of which reduces the value of a stone, are principally impure 

 colour, fissures in the direction of cleavage (" feathers "), and turbidity. Cavities, eithei- 

 vacuous or filled with liquids of various kinds, are also frequentiv present. 



The artificial production of topaz has not at present been achieved with certainty. 

 Good imitations of topaz can be made by fusing strass with a certain amount of glass of 

 -antimony (antimony oxide) and with a trace of purple of Cassius (a compound containing 

 gold), or with a little iron oxide. Purple of Cassius gives a darker, more reddish-yellow, and 

 iron oxide a paler yellow. Such imitations may be distinguished from genuine stones by 

 their single refraction, lower specific gravity, much lower degree of hardness, and by the 

 •entire absence of dichroism. 



Topaz occurs commonly in the old crystalline silicate rocks, namely, in gneiss and 

 crystalline schists as well as in granite. The crystals are attached to the walls of cavities or 

 crevices in these rocks and are often accompanied by tin-stone (cassiterite), aquamarine 

 (beryl), &c. The general conditions of the occurrence are such that topaz must be 

 regarded as the product of fumarole action, the mineral having probably been formed by 

 the interaction of vapours containing fluorine, which were liberated in crevices at the time 

 of the intrusion of the igneous rock. By the weathering and breaking down of the 

 mother-rock the topaz crystals are set free, carried away with the debris, and, as 

 rounded pebbles, find a final resting-place in the alluvial deposits of rivers and streams. 

 In recent years topaz crystals have been met with in the drusy cavities of later volcanic 

 rocks, such as rhyolite ; this is a much less common mode of occurrence and has no 

 commercial significance. 



Topaz of gem-quality occurs at several localities, many of which have already been 

 briefly mentioned, but must now receive more detailed consideration. 



The most important European locality is the Schneckenstein, near Gottesberg, in the 

 neighbourhood of Auerbach, in Voigtland, Kingdom of Saxony. The Schneckenstein, 

 which is situated four kilometres south-east of the railway station of Hammerbriick, is a 

 steep wall of rock projecting from the suiTounding mica-schists, and in appearance 

 resembling an old ruin. It consists of comparatively small fragments of schists rich in 

 tourmaline, cemented into a firm and hard mass by quartz and topaz; the whole rock-mass 

 is known as a topaz-rock. Crystals of topaz, together with quartz, tourmaline, &c., are 

 attached to the walls of cavities in this rock, and the cavities are often partly filled up with 

 white or yellow kaolin. A portion of the wall of such a drusy cavity is represented in 

 Plate XIII., Fig. 3. The free ends of the topaz crystals have a moderately complex 

 termination, the terminal faces including a large basal plane (Fig. 66 d). The crystals 

 vary in size, the smallest having a length and thickness of a few lines, while the largest 

 measure 4 inches in length and 2 inches in thickness. The majority have a length and 

 thickness of about f inch ; larger crystals are rare. 



In colour these topazes are mostly pale wine-yellow, rarely a dark wine-yellow, colourless 

 or white ; the darker the colour the more valuable is the stone. Crystals of a greenish 

 tint, known as " Saxon chrysolite," are sometimes met with ; those of a pure yellow are 



