| Figure
109 Crystal of roepperite showing the forms b(010), m(110), d(101), k(021), e(111), and f(121). Sterling Hill. |
 |
Roepperite |
| (Fe,Mn,Zn,Mg)2SiO4 |
| Orthorhombic |
Forms
c(001), a(100), b(010), m(110), d(101), k(021), e(111),
f(121), and w(211)
| Forms | Localities | Illustration | |
| 1 | b, m, d, k | Sterling Hill | |
| 2 | b, c, m, d, k | Sterling Hill | |
| 3 | b, c, m, d, k, e, f | Sterling Hill | Figure 109 |
| 4 | b, m, d, k | Franklin |
Physical properties
Roepperite, is found commonly in crystals, either prismatic or tabular
parallel to the brachypinacoid. They are rarely sharp, the terminations
being rounded and uneven or the faces being notched and grooved, as if
by solution. It is found also in massive granular form. The cleavage is
perfect parallel to the base and to the brachypinacoid and splintery parallel
to the macropinacoid, and the cleavage surfaces show a greasy luster.
The. exterior of the crystals is black, but broken surfaces are dark green
mottled with yellowish green and the mineral is translucent. The hardness
is 5.5 to 6, and the specific gravity is 3.95
to 4.08.
Roepperite is optically negative; 2V = 77° ±5° ; r > v (rather strong); a = 1.758, b = 1.768, g = 1.804, all ±0.003 (Larsen).
Composition
Roepperite is a member of the chrysolite group, characterized by a high
content of iron and zinc. When described it was the first known zinc-bearing
member of the group, but tephroite has since been found to have so wide
a range in content of zinc that no sharp line can be between the two.
|
1 |
2 |
3 |
|
| SiO2 |
30.76 |
30.23 |
30.54 |
| FeO |
33.78 |
35.52 |
34.78 |
| MnO |
16.25 |
16.91 |
17.74 |
| ZnO |
10.96 |
10.68 |
9.48 |
| MgO |
7.60 |
5.63 |
6.09 |
| Insoluble (spinel) |
1.04 |
2.02 |
|
|
99.35 |
100.01 |
100.65 |
| 1. Crystals. |
| 2. Average of two crystals. |
| 3. Average of two powders of the massive variety |
Occurrence
Roepperite was first described by Roepper (94) and was named for him by Brush
(102). It was named "sterlingite" by Kenngott at the same time,
but the flame "roepperite" was finally adopted. The type material
was found associated with franklinite, jeffersonite, and gahnite. According
to Mr. Canfield, there was a large deposit of it high on the east leg of the
ore body at Sterling Hill, more than 100 tons of which was mined and shipped
as iron ore. It was not noticed at the time, however, as a new or peculiar
mineral, and the deposit was exhausted without many specimens having been
saved. Roepper's specimens were stray fragments picked up years later. The
best specimens seen are in the Canfield collection (see figure 109
and plate 15, A),
where there are single crystals as much as 5 inches long and 2 inches broad,
as well as groups of crystals implanted on the matrix.
| Figure
109 Crystal of roepperite showing the forms b(010), m(110), d(101), k(021), e(111), and f(121). Sterling Hill. |
|
At Franklin Brush (100) identified roepperite in association with gahnite from the tunnel from the Buckwheat mine to the Wallkill River. It is in black crystals that are dark green on fractured surfaces. Brush did not publish his partial analysis, and little of the material was preserved.
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Website
© by Herb Yeates 1997-2006.
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