224 XINIVERSITY OF VIRGINIA PUBLICATIONS 



Evansite* is a hydrated alumina phosphate having approximately the 

 composition expressed bj^ the fonnula Al3(OH)6P04.6H20. It is one of a 

 series of alumina phosphates among which are: 



Turquois A1P04A1(0H)3+H20 



Wardite 2AI2O3.P2O6.4H2O 



Sphaerite 4A1P04.6A1(0H)3(?) 



Lisheardite (Al.Fe) ASO4.2 (AlFe) (OH)3+5H20 



Coeruloloctite 3AI2O3.2P2OS.IOH2O 



Other hydrated alumina phosphates whose chemical composition differs 

 from eA^ansite only in the manner in which are proportioned the ingredi- 

 ents characteristic of each are as follows : 



Augetite 2AI2O5.P2O6.3H2O 



Berlinite 2Al2O3.2P2O5.H2O 



Trolleite ! 4AI2O3.3P2O5 SHjO 



To this list might be added also attacolite (P2O3 . AI2O3 . MnO . CaO . H.2O, 

 etc.) but for its content of manganese oxide, for evansite too, like attaco- 

 lite, contains a small and varying amount of lime. 



The physical appearance of evansite ranges from massive to reniform 

 and botryoidal, and in color from milk-white to dark red and yellow, some 

 specimens being also slightly bluish, translucent and semi-opaque. Its 

 fracture is subconchoidal; and its hardness slightly greater than calcite — 

 the hardness of evansite being about 3.5. According to Forbes,! there is 

 a considerable range in density, the faint yellow varieties being the heaviest. 

 He gives the following table of densities : 



Detisities of Evansite. 



Colorless — translucent 1.822 



Colorless 1.872 



Faint yellow 2.099 



Semi-opaque 1 . 965 



Average density 1.939 



Other determinations of density have been made by SmithJ and also 

 by Kovar.§ In the case of the figure (1.842) for densitj^ furnished by the 



* Text Book of Mineralogy, p. 573, E. S. Dana, 1904. 

 t Philosophical Magazine, vol. 28, p. 341, 1864. 

 t Proc. Royal Soc. N. S. W., vol. 27, p. 382. 

 § Abh. Bohm. Akad., vol. 15, p. 1. 



