96 Cross and Eakins — New occurrence of Ptilolite. 



rocks. The larger part of this area carries minute quantities 

 of gold and silver, the latter predominating, the ratio being 

 1 : 6 by weight. 



Native gold is but seldom associated with barite, and only, 

 as far as I am aware, in silver-gold deposits in which the 

 former metal predominates. Barite is a rare mineral in Cali- 

 fornia, and does not occur in the normal gold quartz veins. 

 Native gold with barite is mentioned as a rare occurrence from 

 southern Colorado,* and Mr. Hanks, in his description of Cali- 

 fornia minerals,f refers to a specimen of barite with gold 

 from the Malakoff hydraulic mine, near North Bloornfleld, 

 Nevada County. It may be stated in this connection that 

 there is a deposit of barite in clay slates seven miles east- 

 northeast of North Bloomfield and cropping out on the North 

 Bloomfleld ditch. I am not aware, however, that it contains 

 any gold. 



Another instance of gold connected with barite is found in 

 Yuba County at the junction of the North and Middle Yuba 

 liivers. A streak of chloritic schist, about twenty feet wide, 

 is here impregnated with pyrite and chalcopyrite and traversed 

 by seams of calcite and barite carrying the same minerals. 

 The brown surface croppings carry native gold, but it is prob- 

 ably all derived from the decomposition of the pyrite. 



IT. S. Geological Survey, Washington, D. C, April, 1892. 



Art. XIII. — A new occurrence of Ptilolite • by Whitman 

 Ceoss and L. G. Eakins. 



In this Journal for August, 1886, we described the first ob- 

 served occurrence of a new hydrous silicate of alumina, lime 

 and alkalies, to which we gave the name ptilolite. The min- 

 eral was remarkable for its high percentage of silica, the analysis 

 leading to the formula B/Al 2 Si 10 O 24 . 5H„0. Inasmuch as the 

 polysilicic acid of this formula was elsewhere unknown, Prof. 

 P. Groth;}; expressed the belief that the material analyzed 

 must have been contaminated with chalcedony, upon which 

 the ptilolite was deposited. While it has seemed to us that the 

 care exercised and the method used in the purification of the 

 original ptilolite material analyzed must exclude the possibility 

 of such contamination, we are glad to be able to announce a 

 second occurrence of this interesting mineral the investiga- 



*See the interesting paper by Mr. R. C. Hills, "Ore Deposits of Summit Dis- 

 trict. Colorado," Proc. Col. Scientific Soc, vol. i, p. 24. 



f Fourth Annual Report California State Mining Bureau, p. 78. 

 % Tabellarische Uebersicht der Mineralien, 2d ed., p. 149, 1889. 



