A REVIEW OF THE AMORPHOUS MINERALS 533 



water. Monite also contains the sulfate radical, but this is not 

 present as gypsum, as Shepard thought, for the mineral is homo- 

 geneous except for minute crystals of monetite and colloform crusts 

 of dahllite. The sulfate radical probably replaces part of the 

 carbonate radical. Phosphorites from Idaho and South Carolina 

 also contain the sulfate radical. 



Nauruite described by Elschner 1 from the island of Nauru is 

 another synonym of collophane. It is a yellow to brown resinous 

 mineral occurring as agate-like layers in cavities of phosphorite. 



The formula given is 3Ca 3 P 2 08— ] p V, > . The analyses of the 



Nauru phosphorites all show calcium carbonate, and specimens of 

 typical nauruite kindly furnished by Mr. Elschner effervesce 

 vigorously in hot nitric acid. Under the microscope the Nauru 

 collophane shows banded spherulitic structure and weak double 

 refraction. The index of refraction is 1 . 597=^0. 001, which proves 

 that the mineral is not dahllite in spite of its birefringence. The 

 double refraction is variable and is lost upon heating. 



I have examined thin sections of phosphorites or so-called phos- 

 phate rocks from Florida, South Carolina, Tennessee, Kentucky, 

 Idaho, Nauru, Fanning Island, Ocean Island, Lassa Island, and 

 Clarendon, New Zealand, and have found amorphous collophane 

 to be the principal constituent of all of them. It is often accom- 

 panied by dahllite. It seems strange that so little attention has 

 been paid to these carbonophosphate minerals, for they are impor- 

 tant from both the economic and scientific standpoints. 



Evansite. Al 3 (OH) 6 P0 4 - (H 2 0)*? — Evansite, a hydrous alumi- 

 num phosphate described by Forbes in 1864, is a typical amorphous 

 mineral. It occurs as a colloform incrustation and greatly resembles 

 allophane. The index of refraction determined on a specimen from 

 Zelegnik, Hungary, is 1. 483 =>= 0.003. 



Evansite has recently been described from two American locali- 

 ties (Goldburg, Idaho, and Columbiana, Alabama) by Schaller. 2 



Pitticite. FeAs0 4 , Fe 2 3 ?(H a O) iB ?— Pitticite is a dark-brown 

 massive mineral resembling limonite. It is a basic ferric aresenate 



1 Corallogene Phosphat-Inseln Austral Oceanien und Hire Produkte (Liibeck, 1913), 

 P- 54- 



2 Bull. 4QO, U.S. Geol. Surv., 191 1, p. 94. 



