A REVIEW OF THE AMORPHOUS MINERALS 531 



the kollophan of Sandberger. Collophane 1 is a calcium carbono- 

 phosphate approaching the formula given above. When the 

 mineral was first described, the calcium carbonate present was 

 thought to be an impurity and so was deducted from the analysis. 

 The chemical composition, as with most amorphous minerals, is 

 variable and somewhat uncertain, because it is difficult to dis- 

 tinguish mechanical impurities from essential constituents. 



Fluorin is present in some specimens, and Lacroix uses the 

 name fluocolophanite for varieties rich in fluorin. Artini 2 describes 

 an amorphous mineral in the phosphorites of Es Salt, Palestine, 

 which he says is a fluorcollophanite near fluorapatite in composi- 

 tion. I have found that fossil bones consist of the mineral collo- 

 phane, and Carnot 3 has shown that the fluorin content of fossil 

 bones increases with the geological age of the bones. If there is an 

 amorphous equivalent of fluorapatite, should a distinctive name, 

 such as fluocollophane, be used for it ? As more latitude must be 

 allowed in the chemical composition of amorphous minerals than 

 in the crystalline minerals, it hardly seems advisable to use more 

 than one name (collophane) for amorphous equivalents of minerals 

 of the apatite group. The fluorin determination is not an accurate 

 one, and fluorin in analyses of the phosphorites may be due to 

 fluorite or residual apatite. 



Collophane is a massive mineral and often has oolitic or con- 

 cretionary structure. In cavities it appears in colloform crusts 

 and often resembles opal. The color is sometimes white, but is 

 usually yellow, brown, or black, and is probably due to an organic 

 pigment. 



Collophane is isotropic in part, but frequently shows double 

 refraction. In a specimen of phosphorite from Lassa Island the 

 double refraction of the colloform collophane is greater than that of 

 the accompanying fibrous dahllite. I have examined specimens 



1 Dana changed kollophan to collophanite, but since the name has not come into 

 general use it is preferable to use the English equivalent of the original, which is a 

 simpler and more euphonious name. Another argument is that collophanite may be 

 confused with colophonite, a variety of garnet. 



2 Abstract in Zeit.f. Kryst. u. Min., LV (1915), 320. 



3 Ann. de Mines (9), III (1893), 155. 



