480 PROCEEDINGS OP THE AMERICAN ACADEMY. 



the barium-mercury-iodide solution, for tlie others about f of a gram. In 

 I. the mineral was decomposed by HCl alone, in the others after pre- 

 vious fusion with Na.jCOs. Iron was first precipitated as basic acetate, 

 then the zinc as sulphide, dissolved and re-precipitated as carbonate, the 

 manganese as sulphide and carbonate, calcium and magnesium, as usual. 

 The manganese carbonate in I. was accidentally contaminated and is in- 

 accurate. Taking III. for computation, in V. it is recalculated to 100, 

 omitting iron and ignition as non-essential. VI. and VII. give the mo- 

 lecular ratios from which we deduce (ZnMn)O : (CaMg)O : SiOs as 

 1:2:2 with Mn to Zn and Mg to Ca as 1 to 15 respectively. The 

 formula is hence (ZnMn)O, 2 (CaMg)O, 2 SiO. or ZnO, 2 CaO, 2 SiO.,. 

 VIII. gives tlie theoretical composition of the latter, and IX. of the 

 former. The mineral gives off a little chlorine with liCl indicating a 

 higher oxidation for some of the manganese unless due to traces of 

 franklinite, and the ferric iron may also be due in part to that impurity. 



Crystal System and Physical Characters. — The grains have no dis- 

 tinct crystalline boundaries, but show several cleavages. Thin sections, 

 prepared by scattering the grains in balsam and grinding thin with em- 

 ery, give in polarized light numerous basal sections which show a distinct 

 uniaxial cross (without any perceptible opening into hyperbolas) and neg- 

 ative optical sign. These basal sections show two distinct sets of rec- 

 tangular cleavages apparently normal to the base, and at 45° to each 

 other, one a little better than the other. Prismatic sections show a good 

 basal cleavage (i. e. normal to the negative optical direction) and par- 

 allel extinction, with a strong bi-refringence. The mineral is therefore 

 tetragonal with a good basal cleavage and secondary cleavages parallel to 

 the prisms of the first and second orders. The specific gravity determined 

 with the pycnometer on over a gram of the material used in Analyses 1. 

 and IV. was respectively 3.397 and 3.395. Hardness between 3 and 4, 

 color white to transparent, with a glassy lustre. Pyrognostics: unaltered 

 in the open and closed tubes. It fuses in the forceps with difficulty to a 

 cloudy glass, giving an intense red calcium flame, especially when moist- 

 ened with HCl. On charcoal the powdered mineral glows intensely, and 

 gives a heavy zinc coating, which is intensified by using NaoCOg, the 

 centre of the assay is then colored bluish green (Mn). A manganese 

 reaction with borax ; gelatinizes easily with HCl. Aside from the crystal 

 system it may be separated from willemite by the hardness, negative 

 optical character, and intense calcium flame. 



The mineral is named Hardystonite from Hardyston township, in which 

 the Franklin mines are situated. 



