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MINERALS INDEX
Hardystonite |
| Ca2ZnSi2O7 |
| Tetragonal |
Physical properties
Hardystonite is found in granular masses and in isolated grains in limestone,
and crystals are not known. The cleavage is good parallel to the base and
poor parallel to both prisms, and cleavage fragments may thus have a prismatic
or even a cubic appearance. The hardness is 3 to 4, and the specific gravity
is 3.39. The mineral is white to faintly pinkish, semitransparent, and has
a vitreous luster. Under the iron-are spark gap it fluoresces a dull, faint
violet or not at all. It is optically negative; the refractive indices are,
for sodium light, w
=1.6691 and e
= 1.6568; for lithium light, w
= 1.6758 and e
= 1.6647, both ±0.0002.
Composition
Hardystonite is a calcium zinc silicate allied to the tetragonal lead silicate
ganomalite. It may contain small amounts of magnesium and manganese in place
of part of the calcium and zinc, respectively.
|
1 |
2 |
3 |
4 |
|
| SiO2 |
38.10 |
37.78 |
36.59 |
38.30 |
| Al2O3 |
0.91 |
0.77 |
||
| Fe2O3 |
0.57 |
0.43 |
||
| FeO |
0.42 |
|||
| ZnO |
24.30 |
25.38 |
22.47 |
25.94 |
| MnO |
1.50 |
1.26 |
1.23 |
|
| CaO |
33.85 |
34.22 |
35.16 |
35.76 |
| MgO |
1.62 |
0.26 |
1.47 |
|
| K2O |
0.78 |
|||
| Na2O |
1.10 |
|||
| PbO |
1.99 a |
|||
| Ignition |
0.52 |
0.34 |
||
|
100.46 |
100.46 |
100.00 |
100.00 |
| a Jenkins and Bauer state: "we have found from 0.66 to 3.55 percent of lead oxide in all the hardystonite analyzed." |
| 1. Grains separated from massive granular ore by heavy solution. J. E. Wolff (185), analyst. |
| 2. Coarse columnar masses. J. E. Wolff (185), analyst. (Minute inclusions seen in thin section may account for the large amount of alkalis found.) |
| 3. Hardystonite, specific gravity 3.443. Jenkins and Bauer (243), analysts. |
| 4. Composition computed from the formula. |
The ratios, shown in the analyses, of ZnO to CaO to SiO2, are close to 2 : 1 : 2, leading to the formula Ca2ZnSi2O7. The lead is probably present in a calcium larsenite molecule.
Occurrence
Hardystonite was discovered and described by Wolff (185), and little has
been added to his observations. It was first found in the Parker shaft at
a depth of about 900 feet, in granular mixture with willemite, rhodonite,
and franklinite. Later it was found in considerable abundance in several
parts of the ore bodies worked through the Parker shaft, but it has not
yet been identified from any other part of the deposit at Franklin. Masses
of several pounds weight and of coarse columnar texture, free from any other
mineral, have been found. It has also been seen associated with brown vesuvianite,
with complex crystals of brown apatite, and intimately intermixed with franklinite
and bright-green. willemite. It appears to have been formed under the influence,
of the pneumatolytic conditions prevalent somewhere in that part of the
mine, which developed such a, peculiar assemblage of minerals as is scarcely
known elsewhere.
The presence of lead, shown by Jenkins and Bauer to exist in all hardystonite, is of economic importance, as it is injurious to the quality of the zinc produced from the ore. Hence the presence of all minerals contain lead is carefully checked in the assay office at the mines.
The composition of hardystonite is closely analog to that of melilite, and X-ray examination shows that the unit cell, space group, and atomic arrangement the same in the two minerals, which differ only in that hardystonite contains zinc in the place of magnesium-aluminum.
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Website
© by Herb Yeates 1997-2001.
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This
page created: January 12, 2001 6:22 PM
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