DEc., 1908. MINERALOGICAL NOTES 137 
the Albany material in the Museum is 10 mm. long, ro mm. wide and 
2mm. thick. Some crystals seen must have been even larger than 
this but they were broken in excavating. The crystals in cavities 
are as a rule smaller than those attached to quartz, their average size 
being 3x3x1mm. The attachment of all the crystals is always 
along an edge parallel with the vertical axis. They thus rarely show 
more than half the faces belonging to the prismatic zone. Their out- 
line tends to be rectangular or hexagonal, according as the lateral pin- 
acoids or the prisms predominate. The orientation adopted for the 
crystals for measurement was determined by the basal plane and by a 
pinacoidal cleavage normal to this which was regarded as that of the 
brachypinacoid, b (oro). The distinctive characters of the base are 
its pearly luster and striations || toa (100). In addition to the cleav- 
age || to b (o10), a prismatic cleavage giving angles of nearly 60° was 
occasionally observed. The faces of the crystals on casual inspection 
appear bright and would seem to be well suited for measurement, 
but on closer examination their surfaces are found as is usual with 
bertrandite to be uneven and to give elongated reflections. This is 
especially true in the prismatic zone, where nearly all the measure- 
ments give variations between 2° and 3°. - By taking the mean of 
these, however, values were obtained which served for identifying the 
faces. The crystals are not highly modified, only six forms being 
observed, as follows: 
c (oor) a (100) jae sey, 
b (of0o) m (110) #1 (202) 
Of these 7 (203) is new to bertrandite, its determination being based 
on the measurement cA/ = (oor) A (203) =33° 56’. The calculated 
- angle for this form, using the axial ratios of Penfield* is 34°59’ or 
using those of UrbaTt is 34° 48’. While the agreement of measured 
and calculated values for this form is not as close as could be desired 
itis all that can be expected when the imperfections of the planes are 
considered. The measurements upon which the determinations of the 
prisms were based are as follows, these being shown with the values 
calculated from both Penfield’s and Urba’s ratios: 
Observed Calculated 
Penfield Urba 
Moan m” = (110) A (1lo) SA ASE alae ne se per ae 
Poe AST =, (130), A (130) 2.0 THA Oona. Gar. 30" 
Cote ameOwss 2 62005 70) 
I 
Cleavage A cleavage = (110) A (oIo) 
+ Amen OUT IOCl., 1880, 3s 375 De 21 5« 1 GSe LIL Soos E55 DLO. 
