322 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



The beryl of the Altai Mountains is distinguished less for the beauty of its crystals 

 than for their size, prisms with a length of 1 metre {391; inches) and a thickness of 15 

 centimetres being met with. These crystals, which have the usual form, namely, a'hexagonal 

 prism terminated by a basal plane perpendicular to the prism planes (Figs. 62a, and 63), 

 range from sky-blue to greenish-blue in colour, and occur in brown, much fissured quartz, 

 the exact locality being a spot in the Tigirezh Mountains. The mineral is here at the 

 best only translucent, and therefore rarely of use as a gem. 



Of greater importance is the occurrence of beryl in the Nerchinsk district of the 

 province of Transbaikalia in south-east Siberia, Nerchinsk itself being in longitude 

 116° E. of Greenwich on the upper course of the Shilka river, a tributary of the Amur. 

 There are here two stretches of country in which beryl, and especially aquamarine, abounds, 

 the one being the mountain range Adun-Chalon and its southern continuation, the 

 mountains of Kuchuserken, and the other the neighbourhood of the Urulga river on the 

 northern side of the Borshchovochnoi Mountains. 



The variously coloured precious stones which occur at Adun-Chalon (Adun-Tschilon) 

 have been known since bhe year 1723. The output of gems from these deposits was 

 formerly very considerable ; it reached its highest in the year 1796, when no less than 

 5 poods (180 pounds) of pure aquamarine, suitable for cutting as gems, was obtained. The 

 crystals of beryl are found here attached to the walls of cavities in a topaz-rock, which 

 consists mainly of finely granular quartz and small topaz crystals, and occurs as veins 

 penetrating the granite. The aquamarine in these cavities is accompanied by topaz and 

 smoky-quartz, frequently also by other minerals. The highest mountain of the Adun- 

 Chalon range has two peaks, separated by a narrow valley. The western peak is known as 

 Hoppevskaya Gora, that is to say. Schorl Mountain ; it consists almost entirely of topaz- 

 rock, and is scanned from foot to summit with the workings of gem-seekers. The mineral is 

 by no means, however, confined to this mountain, numerous mines being scattered about an 

 area of two square versts in the neighbourhood. These mines are nothing but open pits or 

 trenches of the most primitive kind, without timbering, and never more than three fathoms 

 in depth ; from these, short tunnels are worked in the rock in all directions. Immediately 

 beneath the turf covering the southern slopes of the Hoppevskaya Gora is a layer of loose 

 material, containing much iron-ochre, derived from the weathering of the topaz-rock. In 

 this layer fine specimens of aquamarine, and its customary associate topaz, are to be found. 

 A hexagonal prism of transparent beryl, 31 centimetres (over 1 foot) in length and 

 5 centimetres in diameter, from Adun-Chalon, is preserved in the British Museum collection 

 of minerals. 



The beryls of Adun-Chalon differ from the smooth-faced prisms of the Urals and of 

 the Borshchovochnoi Mountains (or Urulga river) in that the prism-faces are deeply striated 

 (Fig. 62 d). The crystals are, as a rule, greenish-blue in colour, but sky-blue, yellowish- 

 green, wine-yellow, and colourless specimens are met with ; and every degree of transparency 

 is represented. The crystals are often united in groups, which are frequently invested with 

 a thin surface layer of iron-ochre, the substance with which the drusy cavities are, as a rule, 

 filled. 



The country between the rivers Shilka and Unda in the Borshchovochnoi Mountains 

 abounds with fine beryl. A large amount of the mineral was obtained about the middle of 

 the nineteenth century, for the most part from the granite mountains which border the 

 Urulga river, a tributary of the Shilka on its right bank. Beryls from the neighbourhood 

 of the Urulga are remarkable for their size, transparency, and beautiful colour. The 

 majority are yellowish-green, the remainder being variously tinted or colourless. The 



