232 " Larson and Glenn — Minerals of the 



A water determination on this material gave 10.85 per 

 cent and indicates the monohydrates which theoretically 

 contains 10.66 per cent H 2 0. 



MnS0 4 crystallized from solution in a desiccator nnder 

 reduced pressure at 23° C was in well formed tabular 

 crystals that gave inclined extinction when on the flat face 

 or on edge and are no doubt triclinic. Y is nearly normal 

 to the laths and crystals lying on the flat face give an 

 extinction of Z', length 15° ± 1°. They are optically — , 

 2V is rather large, and the dispersion is slight. 



a = 1.495 ± 0.003. p = 1.508 ± 0.003. y = 1.514 ± 0.003. 



Carefully selected crystals wiped dry on filter paper 

 were analyzed and gave 38.1 per cent H 2 0, while the theo- 

 retical value for MnS0 4 . 5H 2 is 37.4. 



It alters slowly on standing to a form that is opt. — , 2V 

 moderate. 



a = 1.513 ± 0.003. p = 1.520 ± 0.003. y = 1.522 ± 0.003. 



This is probably the same as the glassy form of the orig- 

 inal sample. 



Crystals formed at 45° C and drained from the solution 

 are imperfect laths. Lying on the flat face they appear to 

 give parallel extinction with X nearly normal to the flat 

 face and Z parallel to the length ; turned on edge they give 

 extinction Z elongation 5°. They are probably mono- 

 clinic, tabular parallel to (100), and elongated along c. 

 Y = b and Z ^ c = 5°. They are optically — , 2V is 

 rather large. 



a = 1.509 ± 0.003. p = 1.518 ± 0.003. y = 1.522 ± 0.003. 



This is probably the tetrahydrate and is like the form of 

 the original sample. 



A solution evaporated on a water bath gave a very pale 

 pink powder made up of aggregates of minute fibers with 

 the following optical properties: Opt. — (?), 2V large, 

 probably monoclinic with Z = b, Y to elongation varies 

 with color of light and gives abnormal interference colors. 



a = 1.560 ± 0.003. p = 1.592 — 0.005. y = 1.627 ± 0.005 



A water determination of this gave 11.2 per cent and 

 shows that it is the monohydrate which should contain 

 theoretically 10.75 per cent. This is the same as the 

 alteration product in the original sample. 



Natural szmikite (MnS0 4 . H 2 0) from Felsobanya, 



