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Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume VIII (1888-1891)

Hobbs, Wm. H.
Not on cerussite from Illinois and Wisconsin,   pp. 399-400 PDF (495.6 KB)


Page 399


Note on Cerussite from Illinois and Wisconsin.
NOTE ON-CERUSSITE FROM ILLINOIS AND- WISCONSIN.-
                        By WM. H. HOBBS.
  A few years since the University of Wisconsin obtained by purchase
the mineral collections of W. T. Henry, of Mineral Point, Wis., They
consist largely of the minerals associated in the zinc and lead deposits
of southwestern Wisconsin and northwestern Illinois, and comprise the
best series existing from that region. Among the carbonates cerussite
is found, the best localities being Galena, Ill., and several points in Iowa
County, Wis.
  In a number of specimens in the University of Wisconsin collections
the mineral is quite well crystallized- and is always found on the surface
of galenite, where its presence is best explained by the action of car-
bonated waters on the galenite. Cubes of galenite attaining in some
cases dimensions of several inches are half covered by yellowish white
cerussite crystals, which vary in size from a millimetre to more than a
centimetre in diameter. They are stoutly columnar and translucent, with
a color varying from yellowish white to light steel-gray. The faces are
Generally somewhat rounded, especially the terminal ones. The brachy-
axis is the one of principal development, the columnar habit being
given by the planes s, -5N  (012), and u, 2P,6 (021), which have about
equal development. The fundamental .prism M terminates the crystals.
The pyramid t, P (111) appears as a rounding of the combination edge
M: s. Twins parallel to M were frequently observed. Measurements of
the interfacial angles with the goniometer of the Fness Universal-
apparat gave the following results:
                                             Measured   Calculated.
  u  u (2P&  2PN  ) ..........................  1110 2'  1100 40'
  s: s (UPS :BP& ) ............ ..............  1390 54'  1400 15'
  M: M (GOP: c P) ...........................  117f 25'  1170 14'
  t :t (P : P) .................................  1300  129f 30'
  The face t gave no image, the value being the average of a number of
measurements by the shimmer seen when the lens was in place before the
telescope.
,7,, 7 , -                           I     'p
                 i"!. i            : ,,-,%-!,,-,,
-   "    Jurisprudentially,              M rWT7
 Ili;%   -
399


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