WATSON AND GOOCH : VIVIANITE FROM FLORIDA 85 



The refractive indices are : 



a = 1.5S0± 0.003, /3= 1.598± 0.003,7 - 1.627± 0.003. 



The grains are colorless and nonpleochroic under the micro- 

 scope. On fine grinding the powder changes to deep blue, 

 which has similar properties as the pale-green fragments, but is 

 strongly pleochroic, with A" = deep cobalt blue, Y and Z, color- 

 less. Fragments of the deeply colored blue crystals show similar 

 properties and absorption formula as the deep-blue powder of 

 the pale-green fragments. 



A carefully selected sample of transparent pale-green crystals 

 of the vivianite was analyzed with the results shown in table 1. 



TABLE 1 



Chemical Analysis of Vivianite (By S. D. Gooch) 



FeO 32.64 



FeaO. 9.43 



P2O5 29 . 99 



H2O - 105°C 11 .86 



H2O + 105°C 15.84 



SiOo 0. 12 



CaO . 02 



MnO 0.25 



TiOs trace 



100.15 



Specific Gravity 2.693 



Careful chemical tests showed the absence of AI2O3, AlgO, 

 the alkalies (Na20 and K2O), F, SO3, and CO2. Attention is 

 directed in the analysis to the seemingly high percentage of 

 ferric oxide. This constituent is invariably present in blue 

 vivianite in varying quantity, analyses showing it to range up to 

 33+ per cent. The presence of ferric oxide in the colored varie- 

 ties of the mineral has been regarded as due to alteration (oxida- 

 tion), but microscopic examination of the mineral and the very 

 rapid change in color of the streak or powder, suggested that 

 the change might possibly be due to inversion from one form to 

 another. 



jMicroscopic examination of the Florida vivianite indicated 

 that the blue color was not uniform but was developed in or along 

 streaks, apparently fractures or cleavage planes or both. The 



