314 SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



adopted, partly in order to render possible a stricter supervision of the workers and to 

 avoid the loss through thieving of a large proportion of the output. The yield of these 

 mines was on the whole small and extremely variable, the labour of several months being 

 sometimes um-ewarded by a single find, while on the other hand emeralds to the weight of 

 100,000 carats would be found in one day. The places at which workings are commenced 

 are chosen entirely at random, for there is nothing to indicate the probability of one spot 

 being more favourable than another. No really reliable statements as to the total yield of 

 the mines are obtainable, but as far as is known it is very variable ; thus, for example, in 

 the year 1849 it averaged 12,400 carats per month, and in the 'fifties 22,386 carats per 

 annum. 



The most important mine at the present day is situated one and a half leguas to the 

 west of Muzo, in latitude 5° 39' 50" N., and longitude 74° 25' W., of Greenwich ; it is about 

 150 kilometres (ninety-four miles) NNW. of Bogota, and lies 878 metres (2897 feet) above 

 sea-level. It has been worked for a long period, but not uninterruptedly ; it ceased, for 

 example, in the middle of the eighteenth century in consequence of a serious fire, and was 

 only recommenced in 1844. The mine has been at one time worked by the Colombian 

 Government, at another leased to natives or to European companies. In the interest of the 

 whole locality much secrecy is observed in the granting of such leases, so that there are 

 many points on which it is impossible to get information. From 1849 to 1861 the mine 

 was worked by an English company, who paid the Government for this privilege 14,200 

 dollars and 5 per cent, of the net profits. From 1864 to 1875 a French company, under 

 the direction of Gustav Lehmann, paid the Government 14,700 dollars per annum for 

 permission to work all the mines. The number of workei-s employed in the mines has varied 

 at different times from 100 to 300. The stones were at first sent to London, but later were 

 placed on the market at Paris. 



There are several detailed descriptions of the most important of these mines, which 

 agree among themselves very completely. From them we learn that it is situated on the 

 left side of a small mountain valley called Minero, or at the present time Carare, which joins 

 the valley of the Magdalena river towards the north-east. It is 60 metres above the bottom 

 of the valley, and has the form of a funnel, the upper diameter of which measures 200 metres, 

 and the lower 50 metres. On the side towards the mountain it reaches a depth of about 

 120 metres, but on the opposite side only 20 or 30 metres ; its walls are very steeply inclined. 

 The rock in which the mine is excavated is a dark bituminous limestone ; this rests on red 

 sandstone and clay-slates, and contains ammonites, which show it to be of Lower Cretaceous 

 (Neocomian) age. 



The emeralds are found in this rock in " horizontal veins," or, more correctly speaking, 

 in single nests embedded in calcite, which is either dark and bituminous or water-clear like 

 Iceland-spar. A crystal of emerald in such a matrix is represented in Plate XII., Fig. 1. 

 Associated with it are very fine crystals of quartz, some water-clear and others green ; also 

 brilliant, well-developed crystals of iron-pyrites, having the form of pentagonal dodecahedra, 

 green gypsum, rhombohedra of black dolomite, and finally crystals of parisite, a fluo- 

 carbonate of cerium and other rare metals, named after Paris, by whom the mine was 

 re-discovered, and who held a lease of it for many years. 



The emeralds are usually of the finest dark green colour, but paler or almost colourless 

 stones are also found, as well as crystals which are quite black, the latter being specially 

 remarkable for their velvety lustre. Occasionally crystals are found which are green on the 

 exterior but colourless inside. The crystals are classified for trade purposes according to 

 transparency and depth of colour. Almost all have the simple form of a six-sided prism 



