A. F. Rogers — Collophane. 269 



Aet. XXY. — Collophane, a Much Neglected Mineral; by 

 Austin F. Rogeks. 



Collophane, amorphous calcium carbonate-phosphate 

 or carbonophosphate, must rank as one of the important 

 minerals, for it is the main constituent of phosphorite or 

 so-called phosphate rock, the production of which in the 

 United States for 1920 amounted to a little over 4 million 

 long tons, valued at about 25 million dollars. That it is 

 also a common and widely distributed mineral results 

 from the fact that fossil bones consist of collophane, as 

 was announced by the writer 1 in 1917. 



The principal constituent of phosphorite 2 is usually 

 regarded as an impure massive variety of apatite, but 

 those that so treat it fail to realize that a given mineral 

 name connotes certain physical properties as well as a 

 given chemical composition. Apatite is the name used 

 for a hexagonal calcium fmophosphate mineral with a 

 specific gravity of about 3.2 and indices of refraction of 

 1.63-1.65 or in a wider sense for a group of minerals 

 including, in addition to the above, the corresponding: 

 chlorophosphate (chlorapatite), carbonophosphate (dahl- 

 lite), and oxyphosphate (voelckerite), all crystalline and 

 with about the same physical properties. 



Now the chief constituent of most of the phosphorites is 

 amorphous and not crystalline. Both its specific gravity 

 and index of refraction are too low for apatite. It always 

 contains an appreciable amount of water which is 

 lacking in apatite 3 and besides, its carbonate content is 

 much higher than that of apatite. It is clear, then, that 

 the name apatite, either as a species name or a group 

 name, can not be used for the substance under considera- 

 tion. 



Some authors treat the amorphous calcium carbono- 

 phosphate in an appendix to apatite, and do not recognize 

 it as a definite mineral. Dana, for example, in the sixth 



1 Jour. Geol., 25, 531. A paper on the mineralogy of fossil bone is soon to 

 appear in the Williston Memorial Volume. 



2 Hereafter the term phosphorite is used as a rock name instead of the 

 more cumbersome term phosphate rock. 



3 As shown by the writer (Mineral. Mag., 27, 155, 1914), oxygen and not 

 hydroxl replaces fluorine and chlorine in some specimens of the apatite 

 group. To a mineral in which the compound 3Ca 3 (P0 4 ) 2 .CaO predominates, 

 the name voelckerite is used. 



