2145. NOTES ON ALUNITE, FSILOMELANITE, ETC.— WHERRY. 



87 



PHYSICAL PEOPEKTIES. 



Color: Varying from cream (Ridgway's 19'f, yellowish orange 

 yellow with 45 per cent white, broken with 32 per cent neutral gray) 

 to Dresden brown (17'k, orange yellow with 70.5 per cent black, 

 broken with 58 per cent gray). 



Luster: Subadamantine ; subtransparent. 



Structure: Columnar to acicular, and radiated; maximum length 

 of needles observed 2 cm. ; diameter 0.1 to 1 mm. Needles somewhat 

 fractured. 



Hardness: 5. 



Density: 3.52. 



Optical properties: Under the microscope colorless; with crossed 

 nicols shows large, variable extinction angle; in convergent light 

 biaxial. Mean index of refraction 1.89. 



CKYSTALLOGRAPHIC PROPERTIES. 



System : Indeterminate. 



Habit: Long prismatic; no definite terminations observed; prism 

 angle G6° 30'. 



Cleavage: Prismatic, imperfect. 



CHEMICAL PROPERTIES. 



Qualitative tests: Before the blowpipe gives reactions for Ca, Ti, 

 Fe, and Si. Insoluble in HCl, but after fusion with NaoCOa dis- 

 solves, yielding reactions for Ca, Fe, Ti, and Si. 



Analysis, made on 0.75 gram purified as above described; J. E. 

 AVhitfield, analvst : 



1. Eesults of analysis. 



2. The percentages of the constituents corresponding to 3G.40 per 

 cent TiO. in the form of titanite, Ca'' (TiO)"(SiOJ""; amount of 

 latter represented, 89.21 per cent. 



3. Remainder left after subtracting 2 from 1. 



4 and 5. Ratios of 3. (Disregarding the P.Oo, the role of which 

 is entirely unknown.) 



