LAPIS-LAZULI : OCCURRENCE IN ASIA 



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haiiynite is always present in the larg-est amount, ultramarine in small amount, or sometimes 

 completely absent, while sodalite is present in still smaller proportion. The colouring 

 properties of all three substances appear to he equal, so that the appearance of the 

 stone as a whole is not affected by the proportions in which they chance to be present. 



Each of these three silicates is decomposed by hydrochloric acid with the separation 

 of gelatinous silica. The sodium sulphide contained in ultramarine, is decomposed by 

 hydrochloric acid with the evolution of hydrogen sulphide, a gas which has the smell 

 characteristic of rotten eggs. When, therefore, lapis-lazuli is treated with hydrochloric 

 acid the presence or absence of this smell indicates the presence or absence of ultramarme. 

 The fact that these three silicates are all decomposed by hydrochloric acid accounts for 

 the decolourisation of lapis-lazuli when subjected to the action of this acid. 



It should be clear from the foregoing that lapis-lazuli, as it is brought into the market 

 and applied to various ornamental purposes, is a limestone more or less richly impregnated 

 with the pigments mentioned above. 

 It is probable that these, as well as 

 the other mineral enclosures (augite, 

 hornblende, &c.) contained in iapis- 

 lazuli, have been formed by the 

 action of an igneous magma, such, 

 for example, as granite, on lime- 

 stone. Lapis-lazuli is thus what is 

 spoken of as a contact-product, 

 as is the case with certain other 

 minerals already described. 



We must now consider the 

 distribution of lapis-lazuli. The 

 occurrence at many of the places 

 stated to be localities for this 

 mineral is by no means well au- 

 thenticated. In some cases the 

 regions mentioned as localities have 



never been thoroughly explored owing to their remoteness and inaccessibility, and in others 

 they are merely places where the stone is marketed. Nevertheless, there are localities at 

 which the occurrence of lapis-lazuli is well authenticated, and of which details concerning 

 the conditions under which it occurs and the manner in which it is collected are known. 

 The richest and most important localities are situated in Asia, and it is from this source 

 that stones of the finest quality are derived. There is an occurrence of less importance 

 in Chile, South America, and another, still less important, in the neighbourhood of Rome 



and Naples. 



The longest known lapis-lazuli mines are situated in Badakshan in the north-east 

 corner of Afghanistan on the upper reaches of the Amu Darja (river Oxus). The Central 

 Asian occurrence of ruby and spinel already mentioned is in the same neighbourhood, and 

 both localities were visited and described as far back as 1271 by the celebrated Venetian 

 traveller Marco Polo. The mode of occurrence of the mineral and the conditions under 

 which it is collected have been described later by other investigators. 



These ancient mines, which are still being worked, are situated in the upper part of the 

 valley of the Kokcha (Fig. 82), a tributary on the left bank of the Oxus. The place lies to 

 the north of the Hindu Kush, between these mountains and the Chodsha-Mohamed range. 



Fig. 82. 



Occurrence of lapis-lazuli in Badakshan. 

 (Scale, 1 : 6.000,000.) 



