jProsopite, Jeffersonite, Oovellite, etc. 55 



If the assumptions made in the foregoing are justified, the 

 Utah mineral is prosopite, and further evidence is afforded of 

 the correctness of the view established by Penfield that fluorine 

 and hydroxyl can mutually replace one another in many min- 

 eral species, for their relative proportions differ materially in 

 the prosopite from the three known localities. The correctness 

 of the formula as applied to the Colorado and Utah prosopite 

 is, however, predicated, as said, on the unproven assumption 

 that the material analyzed contains some admixed fluorite. 



Jeffersonite. 



Two brown substances associated with franklinite and other 

 zinc minerals from Franklin Furnace, N. J., so alike in appear- 

 ance as to have been taken for the same mineral species, were 

 received from Mr. Geo. L. English. One was a little duller than 

 the other and proved to be a mixture of several minerals accord- 

 ing to Mr. F. L. Ransome of the Geological Survey, largely 

 pseudomorphic after some micaceous mineral. From Prof. 

 Clarke's calculations, based on the following analysis, it might 

 be a mixture of a calcium-aluminum garnet, troostite, and 

 limonite. Si0 2 32*09, A1 2 3 11-12, Fe 2 3 5*16, MnO 15-85, 

 ZnO 16-89, CaO 15-65, H 2 2-15, MgO and alk 112; total 

 100-00. 



The other was of a richer and deeper brown and showed 

 such a pronounced cleavage or parting in one direction as to 

 produce a lamellar structure. The luster was brilliant on these 

 cleavage surfaces. Other directions of cleavage were apparent. 

 The hardness was about 5*5 and the density 3-39 at 21*5° C. 

 Before the blowpipe a fragment fused with difficulty to a light 

 colored blebby glass. Analysis gave : 



Si0 2 51-70 



A1 2 U 3 _ -36 



Fe 2 3 - -37 



MnO. 7*43 



ZnO . 3-31 



CaO 23-68 



MgO -. 1257 



Na 2 -12 



K 2 6 trace 



HO .- -65 



100-19 



TiO a , FeO, P,0 6 absent. 



Neglecting the sesquioxides, alkalies and water, this leads to 

 the ratio Si0 2 : RO — 1 : 1*02, and the formula is that of a 

 metasilicate R/'SiOj. According to Mr. English the material 



