MINERALS INDEX
Schallerite |
| Hexagonal? |
Physical character
Schallerite is found in granular form and no crystals are known. It is provisionally
regarded as hexagonal because of its uniaxial character and its similarity
in composition and other characters to friedelite.
Schallerite is red-brown, with a somewhat waxy fracture surface showing minute cleavage facets with pearly luster. The cleavage is basal, the hardness is about 5, and the specific gravity is 3.368. It is optically uniaxial and negative; w = 1.704, e = 1.679.
Schallerite and friedelite are so similar in general appearance that the only way of distinguishing them is by chemical analysis or by measurement of their optical constants. The higher refractive indices of schallerite serve as a sure means of identifying it.
Composition
Schallerite is a hydrous basic manganese arseniosilicate allied to friedelite.
|
1 |
2 |
3 |
4 |
5 |
|
| SiO2 |
31.20 |
31.44 |
31.82 |
32.42 |
32.76 |
| MnO |
44.20 |
44.70 |
50.20 |
49.21 |
51.68 |
| FeO |
1.33 |
2.12 |
0.62 |
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| MgO |
2.13 |
2.19 |
0.71 |
||
| CaO |
0.36 |
||||
| ZnO |
0.39 |
0.54 |
Trace |
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| Cl |
0.08 |
0.60 |
|||
| As2O3 |
12.24 |
12.25 |
7.50 |
9.01 |
|
| As2O5 |
13.81 |
||||
| Al2O3 |
1.59 |
||||
| H2O |
6.93 |
6.55 |
5.73 |
7.24 |
6.55 |
|
99.99 |
100.22 |
100.00 |
99.89 |
100.00 |
|
| O = Cl |
0.02 |
0.13 |
|||
|
100.20 |
99.76 |
| 1. Schallerite, type 1, Franklin. H. E. Vassar (233), analyst |
| 2. Material of no. 1, reanalyzed. L. H. Bauer (260), analyst. |
| 3. Composition of type 1 computed from the formula. |
| 4. Schallerite, type 2, Franklin. L. H. Bauer (260), analyst. |
| 5. Composition of type 2 computed from the formula. |
The formula for schallerite derived by Bauer and Berman (260) from analysis 2 isMn8[(SiO3)6(OH)1.2(As2O3).7].3H2O.
That analysis made it certain that the arsenic in the mineral is trivalent rather than pentavalent as reported in the original description (233). A trace of chlorine was also found. The composition differs from that of friedelite in that the pyroarsenious acid radical takes the place of part of the hydroxyl and chlorine, the total valency remaining the same. The computed composition given in column 3 agrees well with the result of analysis 2.
The second type of schallerite, with less arsenic, whose composition is given in column 4, yields to Bauer and Berman (260) the analogous formula Mn8[(SiO3)6(OH)2(As2O3).5].3H2O.
The refractive indices and the specific gravity of material of the second type are somewhat lower than in the original type, in agreement with its lower content of arsenic.
Occurrence
Schallerite was found in 1924 by R. B. Gage and was described by Gage, Larsen,
and Vassar (233) and named for W. T. Schaller, mineralogist of the United
States Geological Survey. Most of the specimens known seem to have come from
the same small vein, which cuts ordinary massive ore, is composed of solid
granular schallerite, and is from half an inch to 2 inches thick. The only
other mineral in the vein is a bordering layer, here and there, of calcite.
The mineral is said to have been found at a depth of 700 feet, but the exact
part of the mine is not known.
The second type of schallerite, mentioned in a preceding paragraph, is seen in a vein an inch thick, composed chiefly of fowlerite. On one wall is massive granular schallerite, and similar material is scattered through the rhodonite in rounded masses suggesting crystal individuals but seen, when broken, to be aggregates. This type is distinctly yellower than the original schallerite.
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Website
© by Herb Yeates 1997-2006.
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page created: August 12, 2006 6:52 PM
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