QUARTZ (CARNELIAN) 509 



the action of heat, gradually assume the red colour characteristic of carnelian, owing 

 to the hydrated ferric oxide losing vater and becoming anhydrous. Many stones, 

 which in the natural condition are of a dirty yellow colour and unsuitable for gems, 

 on being heated acquire the fine carnelian colour, and with it a considerable increase 

 in value. 



Stones which contain too small a quantity of iron are always pale in colour and 

 cannot be made to assume the deep flesh-red tint when heated. It is, therefore, desirable 

 in some cases to introduce a little more iron. This is done by immersing the stones in a 

 solution of iron nitrate, made by dissolving some iron needles in nitric acid, or in a solution 

 of iron vitriol, which may be more easily obtained and is just as effectual. On heating, the 

 stones assume the fine carnelian red colour ; care must be taken in all these operations, 

 however, that the temperature does not rise too high, for on strongly igniting carnelian 

 it becomes white and dull, and can then be easily crushed to powder. 



The mode of occurrence of carnelian in nature is the same as that of common 

 chalcedony and of agate, namely, as incrustations with nodular surfaces, and in the 

 cracks and crevices, and especially in the amygdaloidal cavities, of volcanic rocks. On 

 the disintegration of these rocks the rounded nodules or irregular fragments of carnelian 

 remain loose in the ground, or are transported by running water, and finally deposited 

 as rounded pebbles in the sands and gravels of rivers and streams. In this form carnelian 

 is of moderately common occurrence. The material, which is cut and polished in the 

 lapidary works, comes almost exclusively, however, from India, Brazil, and Uruguay, where 

 it occurs and is collected with chalcedony of other kinds, especially agate, the occurrence 

 being described below under agate. The localities at which chalcedony of finer quality 

 occurs will now be enumerated. 



In India blocks of carnelian, weighing as much as 3 pounds, are found in the 

 Rajpipla Hills, at Ratanpur, on the lower Narbada river (P'ig. 33). The material as it 

 is found in the mines may be blackish, olive-green, milk-white, or, in fact, almost any 

 colour except red. This tint is only acquired after the stone has been heated, the 

 heating being effected partly by a long exposure to the sun''s rays and partly by fire. 

 Stones, of which the original colour was olive-green, assume an especially fine tint on 

 heating ; they are much prized, and ai'e largely cut in the neighbourhood of Cambay, 

 near Baroda. 



Deposits of carnelian are worked also on the Mahi river, north of Baroda, and the 

 mineral is found at many other places in the volcanic district of western India, but is not 

 everywhere collected and worked. Moreover, pebbles of carnelian are found together with 

 jasper and other varieties of chalcedony in almost all the rivers. A very similar occurrence 

 to those in western India is that in the volcanic rocks of the Rajmahal Hills on the 

 Ganges, in Bengal, but this appears to be of little commercial importance. 



In South America the best known locality for carnelian is Campo de Maia, 

 fifty miles south of the Rio Pardo, which joins the sea at Porto Alegre, Bi'azil. The stones 

 found in this district are remarkable for their j'egular spherical form. Wherever agate 

 occurs in this region it is accompanied by carnelian, so that the latter is somewhat 

 widely distributed. 



Other places occasionally given as localities for fine specimens of carnelian are situated 

 in Dutch Guiana and Siberia ; also at Warwick, in Queensland. Compared with Indian and 

 Brazilian localities, however, all are unimportant. Numbers of carnelians Avere formerly 

 found in Japan, where they were pierced and strung together as beads, and disposed of to the 

 Dutch, who at one time traded extensively with this country. 



