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)

Combinations on crystals of roepperite
  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.

Analyses of roepperite
(W.T. Roepper (99), analyst.)
 

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.		 fig109.gif (5275 bytes)

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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