. Pierres précieuses, un compte rendu populaire de leurs personnages, l'occurrence et d'applications, avec une introduction à leur détermination, pour les minéralogistes, lapidaires, bijoutiers, etc. avec un appendice sur les perles et le corail. Pierres précieuses ; Perles ; les coraux. Fig. 83. Occurrence de lapis-Iazuli dans le bourhood- du lac Baikal. (Échelle, 1 : 2 450 000.) à l'occasion, l'un qui montre un brillant au centre rouge entouré d'une bordure bleu foncé, mat. Le dernier cas suggère que lapis-lazuli bleu foncé est dérivé par l'altération des matériaux, rouge ou violet et s'il en est ainsi, la pierre bleu foncé d'Badaks

• Contributeur: Central Historic Books / Alamy Banque D'Images
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. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. Fig. 83. Occurrence of lapis-Iazuli in the neigh- bourhood of Lake Baikal. (Scale, 1 : 2, 450, 000.) occasionally one which shows a bright red centre surrounded by a dull, dark blue border. The latter case would suggest that dark blue lapis-lazuli is derived by the weathering of red or violet material, and if this be so, the dark blue stone of Badakshan must be regarded as having undergone more alteration than has the violet and red material of Lake Baikal. The output of these mines is very uncertain, and the working of the deposit is never a very profitable undertaking. Moreover, in new ground there is nothing to indicate the presence or absence of the mineral, and the choice of a favourable spot for fresh excavations is entirely fortuitous. In the narrow valley of the small stream Talaya, which has a length of thirty versts (twenty miles) and flows into Lake Baikal two versts to the south of Kultuk, there are on the left side steep clifl's of white doloraitic lime- stone which in places are overlain by granitic rocks. In the limestone are veins filled with a marly limestone containing scales of mica, blocks of compact limestone, and nodules and fragments of lapis-lazuli (Fig. 84). Up to the year 1853 three mines were being worked in this deposit. The material obtained was poor in quality, however, and after the discovery of the richer deposits on the Malaya Bistraya the mines were abandoned. The mines on the Sludianka stream are situated twelve versts south of the village of Kultuk; they were worked for a very long period, were abandoned for a time on account of the poor quality of the lapis-lazuli and the hardness of the rock in which 'it was enclosed, but later were reopened. Here also the mineral is found embedded in

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