202 Genth, and Penfield — Contributions to Mineralogy. 



light the small splinters show indistinctly an obtuse bisectrix, 

 the plane of the optic axes being- parallel to the longer axis. The 

 longer axis is, moreover, axis of least elasticity. These optical 

 properties indicate orthorhombic symmetry while Raimondi 

 regards the crystallization as probably monoclinic. Hardness = 

 1*5. Specific gravity 2*355. 



Associated with the sideronatrite and sometimes forming 

 veins of about 10 to 20 mm in thickness is a grayish white lam- 

 inated mineral, ferronatrite, which is also often intermixed 

 through the whole mass of the sideronatrite, in minute white 

 particles. If it had not been for the difference in the color of 

 these two minerals it would have been impossible to obtain 

 sideronatrite in a state of sufficient purity for analysis. 



Decomposed by cold water into an insoluble basic ferric sul- 

 phate. The analyses gave 





1. 11. 



III. IV. 



Raimondi's 

 analysis 

 after de- 

 ducting 

 4 26 p. c. 

 V. impurities. 



H 2 at 110° 



SOs 



9 ' 42 Ul-61 [1^051 at 110° 9-47 ) [16-67] 

 P i01 44-02 j-oid* 4441 



17-77 16-02 

 45-16 



Fe 2 0, 



21-63 22-54 



21-24 21-66 



22-55 



CaO 



not clet'd not det'd 



not det'd 





Na 2 



1632 16-39 



1591 16-94 



16-27 





99-56 100-00 



9S-49 100-00 



100-00 





Mean. 



Molecular ratio. 



Calculated. 



RoO . 



17 07 



0-948 7 or 7 

 0533 3-92 4 

 0-136 1 1 

 0-264 1-94 2 



. Fe a S 9 0,+7H a O. A 



17-26 



S0 3 



44.22 



43-84 



Feo0 3 . 



21-77 



21-92 



Na 2 . 



16-39 



16-98 



giving the formula : 2Na.,SQ 4 

 about 4 molecules of water. 



t 110° loses 





3. Ferronatrite, 



J. B. Mackintosh.* 





This occurs in cleavage masses, white to grayish white in 

 color. No distinct crystals were observed, but from the cleav- 

 age and optical properties the crystallization must be hexago- 

 nal. The cleavage is prismatic, perfect, the angle between 

 cleavages measuring 60° 2 7 , 59° 58' and 60° 5' where the sur- 

 faces were quite perfect and the reflections sharp ; a number of 

 other angles were measured, all approximating to 60°. A sec- 

 tion cut at right angles to the vertical axis showed in conver- 

 gent polarized light the interference figure of a uniaxial min- 

 eral, and with a quarter undulation mica plate positive double 

 refraction. A prism cut with its edge parallel to the vertical 

 axis yielded with yellow light (soda flame) the following indices 

 of refraction, a» = 1-558, £ = 1*613 indicating rather strong 



* This Journal, III, xxxviii, p. 244, 1889. 



