238 
IOWA ACADEMY OF SCIENCE 
brown spar, well formed crystals of barite are found. They 
are small and few of them are as much as an inch in len^h. 
Grant has noticed that barite, where it occurs at all, appears 
in the main in the vicinity of the oil rock. It is not common, 
but in certain of the mines it is abundant.^ A. J. Williams 
of the Department of Geology of the University of Iowa reports 
having found one well defined crystal of barite in a quarry well 
within the southwest city limits of Dubuque. He also reports 
crystalline barite, which has been much water worn, as having 
been found in the stream beds in the vicinity of Dubuque. The 
crystals upon which this paper is based are found, per- 
fectly developed, at or just below the contact of the Maquoketa 
shale and the upper thin bedded member of the Galena dolomite. 
CHARACTERISTICS OP THE BARITE PROM HANOVER, 
IliMNOIS. 
General Character . — The specimens of barite examined by the 
writer occur in three different forms. The first is the white 
massive form, which is embedded in a matrix of hard compact 
dolomite. It is opaque to transparent and shows good cleavage. 
The second form occurs as an aggregate of crystals. The third 
form is present in distinct crystals varying from seven-tenths 
of an inch to three inches in length along the c-axis. These 
crystals are in some cases found embedded in the limestone^ and 
since this is harder than the barite the crystals' of the latter are 
removed with difficulty. Or they are found in small pockets 
or cavities, from which they are readily removed. Upon exam- 
ination of the crystals several striking features are noticed. 
First is their drusy appearance and paralled growth. In some 
specimens the entire crystal is studded with numerous fine crys- 
tals. In other specimens the drusy appearance is seen only on 
certain faces, and in such cases the macropinacoid faces usually 
are free from the minute crystals. The parallel growths are 
very common and are present in the form of tabular or platy 
crystals parallel to the macropinacoid face. These crystals are 
^exceedingly thin and show domes and prisms. The prisms are 
msiaally very long and linear. Their edges have a crested or 
(COcks-comb-like appearance, due to the projection of distinct 
crystals ; in a few specimens this form of edge may make up the 
entire prism face. Another interesting feature of the crystals 
^U, S. Geol. Survey Bulletin 294/ Lead and Zinc Deposits of the Upper 
Mississippi Valley, page 52. 
