68 FLORIDA GEOLOGICAL SURVEY SIXTH ANNUAL REPORT. 



has been applied to the massive amorphous deposits of phosphate 

 which may be compact, earthy or concretionary. Among other 

 varieties of apatite may be mentioned, staffehte, which contains a 

 small percentage of both iron and aluminum. It is of interest 

 to note also that this variety is believed to result from the action 

 of carbonated waters on phosphorite, and hence is likely to occur 

 incrusting ordinary phosphate rock acted upon by carbonated wa- 

 ters. Another variety, pseudoapatite, contains both sulphur and 

 carbon dioxide.* Of the many other calcium phosphate minerals 

 some closely approximate apatite while others grade into com- 

 pounds so variable and indefinite in composition as scarcely to be 

 classed as minerals. The deposits of phosphate found in nature 

 evidently contain a number of calcium phosphate minerals, the 

 constituent impurities of which affect the market value of the 

 rock. The aluminum phosphate. wavelHte. should also be men- 

 tioned since it is mined to some extent as a source of phosphorus. 



ASSOCIATED MINERALS. 



Various other minerals are found associated in nature with 

 the calcium phosphates. This association is sometimes due to actual 

 relationship between the minerals. On the other hand the associa- 

 tion of minerals may be purely accidental, or incidental to the man- 

 ner of formation of the deposits. With regard to the related 

 minerals, it is apparent that where the calcium^ phosphates are abun- 

 dant, other phosphates are likely also to occur. In fact it is 

 scarcely to be expected that extensive calcium phosphate depos- 

 its v^ill be found without the presence of at least a limited amount 

 of other phosphate minerals. This is particularly true of iron nnri 

 aluminum phosphates. These two bases are widely disseminated 

 in niature and, moreover, they combine readily with phosphoric acid 

 to form phosphates. Oi the iron phosphates the mineral vivianite, 

 althoug^h occurring in relatively small quantities, is widely distrib- 

 uted in nature, and may occur in limited quantities in phosphate 



*Dr. Austin F. Rogers, who is investigating phosphate minerals, states 

 that phosphorite, or phosphate rock, seems to be a mixture of two min- 

 erals, amorphous collophanite, largely a solid solution of calcium carbonate 

 in calcium phosphate, and crystalline dahllite, a calcium carbonophosphate with 

 the formula 3Ca3(P04)2. CaC03 analagous to fluorite. The amorphous col- 

 lophanite gradually changes to the crystalline dahllite. (Personal letter of 

 May 23, 191 4.) 



