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MINERALS INDEX
Hetaerolite |
| ZnO.Mn2O3 |
| Tetragonal |
Forms
c(001), p(111)
Crystallographic measurements
Minute pseudo-octahedral crystals with the base, either simple or twinned on (101), as
shown in figure 49, with four individuals grouped about a central crystal, were found in a
few specimens There is generally some inequality in the size of the individuals, and in
many groups some of the five are lacking.
| Figure 49 Twin group of five crystals of hetaerolite, showing the forms c(001) and p(111); four of the individuals twinned to the fifth one on faces of the second-order pyramid. Franklin. A, Plan; B, clinographic projection. |
 |
The crystals, though brilliant, and somewhat faceted; so that measurements are not satisfactory. On one simple crystal, however, four identical readings were obtained for the angle of the pyramid to the base, 57° 55', making the axial ratio a : c = 1 : 1.128. These values differ considerably from the established elements for hausmannite, which are, angle c to p = 57° 32', and a : c = 1:1.155.
Physical characters
The color of hetaerolite is shining black with a dark-brown streak. Below
are given in tabular form for comparison the optical characters, observed
specific gravity, and computed specific gravity (Gladstone and Dale) for the
minerals of this group. The last-named values are a measure of the effect
produced by the introduction of water in the hetaerolite molecule.
|
Optical indices |
Specific gravity |
|||
|
w |
e |
Observed |
Computed |
|
| Hausmannite |
2.46 |
2.15 |
4.86 |
|
| Zinc hausmannite or hetaerolite (Sterling Hill) |
2.35 |
2.10 |
4.85 |
4.810 |
| Hydrohetaerolite (Colorado) |
2.26 |
2.10 |
4.55 |
4.537 |
Composition
A sample of hetaerolite from Sterling Hill of specific gravity 4.85, purified
by Berman, was analyzed and found to have the following composition:
|
Percent |
Molecular ratios |
||
| Mn2O3 |
64.21 |
0.407* |
0.409 |
| Fe2O3 |
0.24 |
0.002* |
|
| ZnO |
32.46 |
0.399† |
0.425 |
| MnO |
1.86 |
0.026† |
|
| MgO |
0.49 |
||
| SiO2 |
0.18 |
||
| H2O |
0.19 |
||
|
99.63 |
|||
| [* Figures reflected in the 0.409 value shown] |
| [† Figures reflected in the 0.425 value shown] |
The composition is that of an anhydrous oxide, and it gives molecular ratios close to those demanded by the formula adopted for the mineral, which is ZnO.Mn2O3.
Hetaerolite is unaltered in the blowpipe flame and yields a zinc coating when reduced with soda on charcoal.
Occurrence
The shining black crystals, none more than a tenth of an inch in diameter,
line druses in thin veins that traverse massive ore. The vein filling is
a massive or platy brown jeffersonite.
The druses are few and contain also brilliant wine-colored and pink hodgkinsonite
crystals, beryl-colored willemite, and calcite. All these are later than
the hetaerolite, and calcite in some places entirely fills the middle of
the vein, forming molds about the crystals of hetaerolite on the walls.
The specimens containing this mineral were brought to the author's attention
in 1914 by Mr. Cahn. The association with hodgkinsonite proves that they
were found in the northern part of the mine at Franklin, the only place
where hodgkinsonite has yet been found.
The crystals from Sterling Hill are unmodified pyramids implanted on massive franklinite and show no twinning.
Historical notes
Hetaerolite was originally found in abundance at Sterling Hill in oxidized
material and was first described by Moore (114) somewhat doubtfully as a
zinc hausmannite. No further examination of the mineral was made until 1910,
when the author published (195) a new analysis by Schaller and concluded
that it is zinc hausmannite, but in doing so he ignored a considerable content
of water that was not accounted for. In 1913 Ford and Bradley (201) described
hetaerolite from Leadville, Colorado, where also it was found amid oxidized
ores. They concluded that it should be regarded as a hydrous oxide, with
the formula 2ZnO.2Mn2O3.H2O, but their
material was impure and to obtain that result 10 percent of calamine had
to be deducted from the analysis.
Bauer analyzed hetaerolite from a new occurrence of the mineral at Sterling Hill (257), where it is associated with unoxidized franklinite. This analysis shows scarcely a trace of water and gives an almost ideal ratio for zinc hausmannite, ZnO.Mn2O3. Thus Moore's original conclusion that the mineral is a zinc hausmannite is confirmed. Under these circumstances it seems quite justifiable to use his name, "hetaerolite", for the anhydrous oxide. The hydrous variety is described on page 53 under the name "hydrohetaerolite."
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Website
© by Herb Yeates 1997-2001.
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This
page created: January 12, 2001 6:23 PM
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