BALLER.l 
ihwiortikrite. 
101 
|Fhe prismatic cleavage was found to be parallel to the prism {210/. 
large number of measurements gave as the angle [010j cleavage 
Icks62 67°, averaging 64 65°. The angle {OIOJ (210} is 66' 01'. 
ho cleavage cracks arc irregular, and it was difficult to obtain any 
pirate measurements, but the ones made are sufficient to determine 
fccleavage. They were measured against the trace of the optic axial 
lane. 
p in one particular section (the same on which the prismatic cleav- 
>v was measured) were determinable to a certain extent. The 
tomato lamella 1 extinguished together, the difference in angle of 
■Inction of two adjacent lamellae being about 31 . The line joining 
Lose lamellae is parallel to the cleavage or to the prism {210J*. The 
■ace of the axial plane is 
millel (or nearly so) in ad- 
cent lamellae. 
The pleochroism of the 
ineral is beautiful, espe- 
ally if the section be not 
>o thin. C— a is colorless, 
== h is colorless to very 
lint pink, it= c is deep-red 
irple. None of the see- 
ms entirely possess the 
•dinarv blue pleochroism. 
some slides, however, 
ere are certain small areas 
varied and irregular shape 
ich do show the ordinary 
eochroism. These small 
ue areas in the rich red- 
|rple background make a most beautiful combinati 
Fig. 6. — Dnmortierite alter 
On some 
M'tions a large area will have a faint bluish-purple color, as if inter- 
ijediate between the deep-blue and the red purple. 
This California dumortierite contains about 1J per cent titanium 
« ide, which is considered as Ti 2 3 , replacing part of the alumina. 
Llrrelating these facts with the other known instances, it seems as it' 
tip presence of the titanium controlled the occurrence of this purple 
ipochroism. Samples of the Washington and Arizona mineral, free 
f|>m titanite and rutile, and which possess the ordinary colorless to 
Hie pleochroism, were tested qualitatively for titanium with hydro- 
f peroxide, with a negative result in each case. One might conclude, 
ref ore, that in those areas of a dumortierite section in which the 
Mor is blue there is no titanium; that they are molecular centers, so 
Hspeak, which are free from titanium. The absorption of the mineral 
