9 
If the refractive indices for collinsite and messelite are plotted with 
respect to their magnesium and iron oxides content it is feasible by extra- 
polation to obtain approximate values of the indices for the possible pure 
end members of the series, that is, the pure magnesian and the pure iron 
compounds {Bee Figure 3). The pure magnesium compound will be 
optically negative and have approximately the following indices: 
a = 1-623; 0 = 1-633; y - 1-640. 
The pure iron compound will be optically positive and have: 
a = 1-648; (3 = 1-667; y = 1-687. 
QUERCYITE 
As already stated the British Columbia phosphorite is composed of 
collinsite, wurtzilite, and quercyite. The name quercyite is given to a 
substance which was found to have the same chemical composition as the 
original material described by Lacroix under that name. 
Another factor which would seem to strengthen the view that the 
British Columbia mineral is typical quercyite is that a microphotograph 
of a thin section made from it (Plate II) is practically identical with a 
microphotograph of French quercyite given by Alfred Lacroix in the 
“Mineralogy of France.” 1 On the other hand the original quercyite is 
described as an admixture of dahllite or francolite, with variable propor- 
tions of isotropic collophanite. Microscopic examination reveals that the 
Canadian quercyite is practically composed of one mineral, probably 
closely related to the fibrous form of francolite. The mean refractive 
Uacroix, Alfred: Tome Quatrieme, 2c Partie, fig. 1, p. 680. 
