CHAPTER V. 



THE MINOR MINERAL INGREDIMENTS OF SOILS; MINERAL 

 FERTILIZERS ; MINERALS INJURIOUS TO AGRICULTURE. 



(A.) MINERALS USED AS FERTILIZERS. 



OF minerals important in soil-formation, not usually present 

 in large amounts in rocks, but extensively used in fertilization, 

 the following require mention: 



Apatite; phosphate of lime containing more or less of the 

 chlorids and fluorids of the same metal ; the mineral from 

 which the phosphoric acid of the soil is mostly derived. In 

 the crystallized condition when perfectly pure it is colorless ; 

 but it is mostly of a greenish tint (hence " asparagus stone "). 

 The pure crystalline mineral rarely occurs in large masses (as 

 in Canada) ; but small to minute crystals are found widely dis- 

 seminated in many rocks (granites, " basalts " of the Pacific 

 Northwest), thus passing into the soils formed from these 

 rocks. These crystals are readily recognized, being regular 

 six-sided prisms with a flat or obtusely pyramidal termination 

 (distinction from quartz), and do not effervesce with acids 

 (distinction from calcite). By far the largest deposits of 

 this mineral occur in connection with carbonate of lime, in the 

 rock materials known as phosphorites. Lime phosphate be- 

 ing, like the carbonate, soluble in carbonated water, the two 

 naturally frequently pass into solution, and are subsequently 

 deposited together. Most limestones contain a small propor- 

 tion of lime phosphate, being, as already stated, formed from 

 the shells and the framework of animal organisms usually 

 containing also phosphates. But the content of phosphates 

 in limestones is not readily apparent to the eye, and the richest 

 deposits, save such as contain animal bones, have long 

 passed unsuspected as to their being anything else but lime- 

 stone. Systematic search has now revealed the presence of 

 phosphate rock in numerous localities, chiefly where limestone 



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