110 0. A. Derhy — Monazite as an Element in Hocks. 



hung to the bottom of the pan behind the black iron minerals. 

 Under the microscope the white grains show the charac- 

 teristic form of zircon while the yellow ones, aside from their 

 physical resemblance to the Bahia mineral, give like that, the 

 didymium band in the hand spectroscope and the microchemi- 

 cal tests for phosphoric acid and cerium, so that their identity 

 with monazite seems clearly established. 



As gneiss is the only rock that is at all abundant about Bio de 

 Janeiro, it was natural to suppose that the mineral so widely 

 distributed in the sands might have come from that rock. 

 About the same time Prince Pedro Augusto de Saxe Coburg 

 Gotha discovered in an apatite-bearing streak of the gneiss of 

 the Serra de Tijuca a minute yellow crystal with the physical 

 aspect of monazite, but too small for chemical tests. This 

 suggested the idea that, notwithstanding the small proportion 

 of the mineral and the microscopic size of the grains, it was 

 not altogether hopeless to look for it in the rock itself, while 

 Mr. Gordon's method of concentration by panning was nat- 

 urally suggested as the simplest and readiest mode of in- 

 vestigating the question. Under Mr. Gordon's instruction I 

 soon acquired sufficient facility in the use of the pan to make 

 a satisfactory concentration and with his aid some scores of 

 tests have been made of the rocks in the vicinity of Bio and 

 from about a dozen points in the provinces of Rio de Janeiro, 

 Minas Geraes and Sao Paulo. Where decomposed rock was 

 obtainable the tests were made on this by washing a quantity 

 equal to a heaped double handful, care being taken to obtain 

 material decomposed in situ and carefully freed from any 

 extraneous wash. Where decomposed material was not at 

 hand pieces of sound rock were ground in a mortar, a fragment 

 the size of the fist or even smaller proving sufficient for a 

 satisfactory test. 



All the tests made on gneiss, granite and syenite have 

 given, in addition to zircon, a greater or less quantity of mi- 

 croscopic crystals of a heavy yellow mineral apparently identi- 

 cal with the Bahia monazite. As no crystallographic study 

 could be made, the identification has been based on the general 

 appearance of the grains, their high specific gravity, and mi- 

 crochemical tests for phosphoric acid and cerium. In some few 

 cases the yellow grains are lighter in color and duller in luster 

 than the Bahia mineral, but as they give the phosphoric acid 

 and cerium reactions they are presumed to represent a variety 

 of monazite, or perhaps some other cerium-bearing phos- 

 phate. Their high specific gravity is proved by their behavior 

 in the pan where they remain with the zircon, behind the other 

 minerals, so that, after extracting the magnetite with a magnet, 

 it is possible by careful manipulation to obtain these two min- 



