182 C. Palache — Mineralogy of Franklin Furnace, N. J. 



a : b : c = "4409 : 1 : -5808 



= -440 : 1 : -566 (Penfield). 

 Forms : a (100), b (010), m (110,) s (120), x (103), h (021) 

 e(Ul),/(121). 



Combinations : 1. b. m. s. x. 



2. a. b. m. s. k. e. f. 

 Calculated Measured 



Angles : , * . , K v 



<t> P <p p 



111 66°12' 55 13 66 13 55 15 2 faces good 



121 48 36 60 12 49 22 60 29 1 face poor 



110 69 12 90 00 66 09 90 00 4 faces good 



120 48 36 90 00 49 14 90 00 poor 



Bementite : Composition, System. 



Tlie description of bementite by Koenig was incomplete and 

 its relations were not clear. Study of a later find of better 

 material from the Parker shaft, Franklin Furnace, establishes 

 its close relationship to tephroite in system and composition. 



System orthorhombic, shown by three pinacoidal cleavages 

 at right angles but unequally perfect ; and by a symmetrical 

 biaxial interference figure witli small axial angle seen on plates 

 parallel to the best cleavage. 



The analysis given below agrees closely with that of Koenig, 

 but the water is shown to be constitutional, coining off for the 

 most part at a red heat. It leads to the formula H 6 Mn 5 

 (Si0 4 ) 4 with more or less replacement of manganese by iron, 

 zinc and magnesium. This is analogous to the formula of 

 tephroite, which may be written Mn 8 Si 4 16 ; in bementite three 

 molecules of manganese are replaced by constitutional water. 

 That it is not a simple case of partial hydration is shown by the 

 optical homogeneity of the bementite crystals. 



1. Analysis of bementite, Geo. Steiger, U. S. G. S., 1906. 



2. Same recalculated to 100 per cent after omitting A1 2 3 , 

 Fe 2 3 and H 2 — and substituting for FeO, MgO, CaO, and ZnO, 

 equivalent amounts of MnO. 



3. Theory for H 6 Mn 5 (Si0 4 ) 4 . 



Si0 2 MnO FeO ZnO MgO CaO 



1 38-36 39-22 494 293 335 062 



2 37-93 53-56 



3 37-18 54-53 



Willemite : Axial Ratio, Refractive Indices. 

 No accurate measurements of willemite crystals from New 

 Jersey have been hitherto recorded. The fundamental angle 

 employed by Dana was based on contact measurements of 

 troostite. Other authors use the element determined by Levy 

 on crystals from Moresnet, on which the sole form is a rhombo- 

 liedron not found on Franklin crystals. A number of measur- 

 able crystals, all from the Parker shaft, Franklin Furnace, 



H 2 + 



H 2 0- 



A1 2 3 



Fe 2 3 





8-01 



0-60 



0-96 



0-71 



99.70 



8-51 









100-00 



8-29 









100-00 



