258 ECONOMIC GEOLOGY 



transformed into wurtzite. An ore body, therefore, containing 

 wurtzite is probably a product of high temperatures. What 

 these temperatures are and at what temperature the transforma- 

 tion of sphalerite to wurtzite takes place remain to be determined. 

 Sphalerite has been produced by the action of decaying wood 

 upon the solutions of zinc sulphate in old zinc mines. According 

 to H. A. Wheeler, the massive blendes occur at North St. Louis, 

 Missouri, embedded in lignite, where these blendes have evidently 

 been formed by the action of organic matter upon soluble zinc 

 compounds. C. R. Keyes reports sphalerite crystals on iron 

 nails that have been immersed in mine waters for 15 years. 

 W. P. Jenney cites the occurrence of sphalerite upon the walls of 

 a tunnel that has been closed and filled with mine waters for 

 several years. Crystals of sphalerite have also been observed 

 upon the pick marks in abandoned zinc mines. Sphalerite in 

 its association with the lead mines of the Mississippi Valley 

 appears to be of secondary origin. 



According to J. D. Robertson, zinc sulphide occurs at Galena, 

 Kansas, as a white mud mingled with acid water. Evidently 

 the zinc was brought into solution by the oxidation of sphalerite 

 and thrown out of solution either by the action of sulphureted 

 waters or by organic matter. 



Smithsonite is a secondary mineral of metasomatic origin. 

 Wherever zinciferous solutions percolate through limestones a 

 reaction follows with the deposition of the zinc as smithsonite 

 in the place of the removed calcium compounds. G. Bischoff 

 reports several instances in which smithsonite has formed as a 

 deposit from natural waters. The alteration of the zinc ores in 

 Missouri and Arkansas has given rise to a zinciferous clay known 

 as tallow clay. 



Zincite and franklinite at Franklin Furnace, New Jersey, form 

 a unique deposit produced by contact metamorphism. This 

 ore deposit will be discussed in detail a little later in this chapter. 



Goslarite is an oxygenated secondary mineral. It occurs as a 

 solid in the Rammelsberg mine near Goslar in the Harz Moun- 

 tains, at Schemnitz in Hungary, and elsewhere. It is formed 

 through the oxidation of sphalerite. It is present in solution in 

 mine waters and zinciferous mineral springs. It is in this form 

 that zinc is leached out of zinciferous rocks and transported 

 elsewhere for subsequent deposition as an ore body. 



Willemite, which has come into prominence through the study 



