RoGERs. | Minerals of the Galena-Joplin District. 495 
to the ragged free edge perhaps represents a clinodome, as 
the extinction is not quite parallel to the vertical edges. 
These crystals are quite like some from Beaverhead county, 
Montana. | 
No chemical analyses were made, owing to lack of sufficient 
material. Penfield’s research” leaves nothing to be desired 
as to the composition of the mineral, the formula for which 
he gives as 2(CuZn) CO; 3(CuZn) (OH ).. 
Hydrozincite ; ‘‘WHITE JACK.”’ 
Hydrozincite has only been found at one locality (Granby) 
by the writer, though it is mentioned from other points of the 
district by previous observers. It occurs as a dull white 
amorphous incrustation, associated with calamine and smith- 
sonite, often as a layer between the two. [Frequently it as- 
sumes a mammillary or stalactitic form made up of concentric 
layers. 
An average of two analyses of hydrozincite from Granby, 
made by Mr. Edgar B. Hayes, gave the following: 
SiOapRy ne ane once” 0.14 Theoretical for ZnCO3-2Zn(OH): 
COnPeR re ee ethane: ABO As SUT Vee cba T a ie 13.60 
OOP Reise sss het es oe DANA AA a ees Eo TO cea 11.10 
ZAIN ON sesir co its es tr te ROO ROOM Me Ae IN atin 75.30 
100.00 100.00 
Calamine; ‘‘SILICATE’’; ‘‘GRAY JACK.’’ 
Observed forms: c(001)OP; a(010)”Po; m(110) oP; 
Q(OlL) Pe ¢ ACBL) s S(O) Pe 2 h(GOM)\ ses p WV (1) PE. 
The calamine crystals are almost invariably flattened paral- 
lel to the faces of the brachypinacoid, which is consequently 
the dominant form. These faces are vertically striated. Oc- 
casionally a crystal is found which exhibits both analogous 
and antilogous poles. The following diagram will serve to 
illustrate the distribution of forms on the different crystals 
examined : 
CRYSTAL. 1 2 3 4 5 6 q 
Analogous pole, | c, e,i,t,s|t,i |t,i,c/t,1 | t,e |s,t,e|t,s,c,e,1 
Paismish as eee a, m 2b, a0) |] 2h 100) |) fy, OO || BY, 100) |), [am |) ly fat 
Antilogous pole, | e, v — —]levfjiev}]— —_ 
17. Penfield: Amer. Jour. Sci., vol. 41 (3), pp. 106-109, 1891. 
