138 FreELD CoLuMBIAN MusEuM—GEo .oey, VoL. III. 
There is little variation in the development of the crystals, the 
principal differences being in the development of the macropinacoid 
a (100). .When this is ‘extended, as shown in Fig) 4, Plo XxEVIT, 
the crystals have a generally rectangular outline; when it is developed 
about equally with the prisms, the crystals have an apparently hex- 
agonal outline if, as is usually the case, only half of the crystal is pres- 
ent. Again the unit prism m (110) may be wanting entirely. If so, 
the crystal is usually elongated in the direction of the macro-axis 
and attached by the brachypinacoid b (o10) so that the appearance 
illustrated in Fig. 5, Pl. XLVII is obtained. This drawing is made 
with b (oro) in front in order to show the characteristic appearance. 
The form 7 (203), as illustrated in the figures, occurs at only one end of 
the vertical axis. The absence of a corresponding plane indicates 
hemimorphism in the direction of the vertical axis such as was noted 
by Penfield.* The edge opposite to / (203) produced by the junction 
of ¢ (ool) and a (100) and that upon which a plane corresponding to 
Z would normally appear if the crystal were holomorphic, is never 
sharp, but grades irregularly toward the center of the crystal by suc- 
cessive overlying lamellae, all of which have irregular edges. Such 
indications of lamellar structure suggest twinning similar to that 
noted by Penfield on crystals from Mt. Antero,} but study of cross- 
sections of the crystals in polarized light gives no evidence to support 
such a view. Extinction in polarized light occurs parallel to the pina- 
coidal cleavage of the crystals, thus affording additional proof of the 
orthorhombic crystallization of the mineral. On slight heating the 
crystals become strongly electric so that they pick up pieces of paper. 
Before the blowpipe they exfoliate slightly and when heated in the 
closed tube decrepitate. The other blowpipe characters observed 
were similar to those which have been mentioned by previous ob- 
servers. . | 
CALAMINE 
LEADVIELES GOLORADG 
Among specimens received by the Museum from the World’s 
Columbian Exposition, a series of ores from the Maid of Erin mine, 
Leadville, Colorado, contained an ocherous substance thickly coated 
with long, slender crystals. These crystals proved on examination 
by means of a blow-pipe to be calamine. The occurrence seems 
not to have been hitherto described, although Pratt has given an 
* Loc. cit. T Loc. cit: 
