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Tephroite Zincite Willemite Calcite & Franklinite

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LMB525391

Tephroite Zincite Willemite Calcite & Franklinite

Type Locality

Description Tabs

Description
Locality: 
Sterling Mine, Ogdensburg, Sussex County, New Jersey, United States of America
Class: 
Combination
Size Range: 
Miniature (4.5-7 cm)
Size: 
5 × 6 × 4 cm
Largest Crystal: 
3.50cm
Weight: 
225.00gr
Description

This is for those with a lot of patience!

Tephroite is a not a rare mineral at the Sterling Mine, but crystals are not common. And crystals that one can see are rare indeed. The problem is two-fold. The best crystals are micro, very rare, and almost always from the Franklin mine, not here. But the more common large crystals are almost always frozen in matrix. Recovering a large tephroite crystal without substantial damage is extremely difficult.

This specimen features several large crystals, the largest about 3.4 cm in maximum diameter. But, except for some small crystals that may still be completely imbedded, there are only cross-sections, not complete crystals. And the crystals are not easy to recognize.

Tephroite is orthorhombic, and the large crystals are prisms with a plethora of prism faces. I have taken the liberty of posting an old Charles Palache diagram (from his famous monograph) illustrating such a crystal under “Analysis”. Because the large crystals are somewhat crude and the edges are not very sharp, the resulting crystals look somewhat like flattened dark rye bread loaves and cross-sections look like “lozenges” (or “lentils”). Perhaps the clearest example of such a “lozenge” on this specimen is the small (1.5 cm) crystal shown just above the franklinite in the first photo. If you have access to Pete Dunn's "Franklin and Sterling Hill, New Jersey: the world's most  magnificent mineral deposits", see Figure 15-9 for very similar crystal cross-sections (except that these are partly rimmed by sonolite). 

The large (3.4 cm) crystal just below the platy zincite is also a “lozenge”, but it has another, smaller (1.8 cm), “lozenge” attached at the bottom which, in turn, has a couple of yet smaller attached “lozenges”. This confuses the basic morphology. But once you know what to look for, you will see that there are yet other “lozenges” on this side of the specimen – and more on the other sides.

So this is a specimen with numerous, fairly large, but partial, tephroite crystals – not masses.

When I was collecting this stuff (ca 1993) at the Sterling Hill Mining Museum Mine Run Dump, I knew nothing about tephroite and thought it was some sort of “grade Z” altering willemite because of the spotty willemite UV response shown in the second photo. In reality, this willemite is an exsolution product of the tephroite and is a very good way to recognize tephroite at the Sterling Mine. (Note that the willimite is not the light colored stuff in the vertical veinlets cross-cutting the tephroite. The willemite is confined to a network of very thin sheets along parting planes in the tephroite, plus an external “rim”. )

Had I known that I was dealing with large tephroite crystals, perhaps a few could have been preserved intact. (More savvy collectors are, no doubt, snorting in derision as they drool over their large, perfect, and carefully hand-excavated tephroites. But we don’t see such for sale – do we?)

The third photo shows the “back” of the specimen and the cross-section of what appears to be a large penetration twin consisting of a “lozenge” (roughly E-W) and a more ordinary “baryite-like” orthorhombic crystal (roughly NE-SW). The maximum diameter is about 2.8 cm. (The “lozenge” is probably the same crystal as seen on the “front”.)

Note: The blue areas in the UV photo are not fluorescence. They are due to a bit of daylight allowed in so as to “outline” the zincite end of the specimen. Incidentally, the franklinite is euhedral – but good luck getting any crystals out of the matrix. One small crystal – about 4 mm on edge – does poke out on one side, but the “tip” is broken.)

This is one of the smaller (but more interesting) tephroites that I have. But it is still “inconveniently” heavy. Single item shipping weight is about 12 oz. If you are planning to hold an "open box" so as to reduce postage costs by combining items from a future auction, please note that USPS postage rates recently changed significantly.

Outside the USA, the stated postage and packing rate applies up to a total weight of 32 oz (225 g).

Within the USA, I will use Priority Mail. Up to 16 oz, the “own box” Priority rate is $8.50 (including packing).

Please see my "Shipping Policy" for details. 

Mineral Data
What's on the rock

Tephroite

Formula: 
Mn2+2SiO4
Strunz: 
9.AC.05
Crystal System: 
Orthorhombic Forms short prismatic crystals.
Hardness: 
6.0
Streak: 
Pale gray
Type Locality: 
Sterling Mine, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex Co., New Jersey, USA

Zincite

Formula: 
(Zn,Mn2+,Fe2+)O
Strunz: 
4.AB.20
Crystal System: 
Hexagonal
Hardness: 
4.0
Type Locality: 
Sterling Mine, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex Co., New Jersey, USA

Willemite

Formula: 
Zn2SiO4
Strunz: 
9.AA.05
Hardness: 
5.5
Streak: 
White
Type Locality: 
Vieille Montagne (Altenberg; Kelmisberg), Moresnet, Kelmis, Plombières-Vieille Montagne District (Plombières-Altenberg), Verviers, Liège Province, Belgium

Calcite

Polymorph of: 
Formula: 
CaCO3
Strunz: 
5.AB.05
Crystal System: 
Trigonal
Hardness: 
3.0
Streak: 
White

Franklinite

Formula: 
Zn2+Fe3+2O4
Strunz: 
4.BB.05
Crystal System: 
Isometric
Hardness: 
5.5 - 6.0
Colour: 
Black
Type Locality: 
Sterling Mine, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex Co., New Jersey, USA
Analysis
Analysis Report - only: Tephroite Zincite Willemite Calcite & Franklinite
LMB minerals

Seller Information

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Seller's terms and conditions

In addition to the standard terms and conditions, please note the following. Almost all IDs are visual. While in most cases the ID is obvious, there may be cases where it is not. If you are doubtful about a particular ID, please ask for more information. Or do not bid! Similarly, if you are not sure that the specimen meets your criteria, do not bid. I have tdone the best I can with the photos. Nevertheless, if you are not happy with a specimen for any reason, I will refund the bid price – but not the shipping costs (unless the fault is clearly mine) – if the specimen is returned. This policy applies even if analysis of the specimen shows that my ID was incorrect. When in doubt, ask - or don’t bid. Note that most crystals at MSH and Varennes are micros - even if on large specimens. Please pay attention to the stated sizes. Any customs duties, fees etc. are the responsibility of the buyer.