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[nurbo]

Hello,
This Hematite comes from Eskdale in Cumbria here in the UK, I just wondered if anyone had seen anything similar? The "Nails" of Haematite show Kidney ore form close up and have formed around a central core,
This piece measures around 40 x 45 x 45 mm.

[nurbo]

A little bit more about these Hematites ... The matrix is heavily altered Haematised Granite and they are pretty much randomly orientated, the cores of the "Nails" can be orientated horizontally with reference to the outer surface or vertically and some have no core at all, I even found one that has a square core that is hollow, the more you try and study these pieces the less sense they make. Ive added a picture of the square core, which isnt brilliant but you can make out one of the corners, also a picture of a Botryoidal shaped core and a photo of a close up of another piece.

[Pete Richards]

I would say these formed around elongated prismatic crystals of some other mineral, which has since dissolved away. This often happens with anhydrite in basaltic environments, but I don't know if that mineral makes any sense for your locality.

[al mar]

An strange form!

I think must be an ancient stalactitic form , the stalactites leave the original matrix and were cemented on a massive iron ore .

However, there are so long.

[bugrock]

Are you sure the elongated structures are hematite? Should give a red streak, best to take a few small fragments and crush to a powder in mortar and pestle. Just from gross appearance could also be goethite or perhaps even a manganese oxide/hydroxide species. They are remarkable whatever their composition.

Also, have you checked the UK literature? There is an encyclopedic book on UK minerals (can't recall title at the moment) and good regional texts.

[Philip G]

Hi all,

I'll try to add a bit more to this as it has puzzled me for quite some time now!

A little bit of background information.

The specimen is from the dumps of the Gill Force Levels, South Cumberland Mine, Eskdale, Cumbria. Definite red streak indicates hematite.

Stalactitic and 'ring ore' hematite recorded from here together with the more common standard kidney-ore types. Previous Cumbrian stalactitic examples i have seen have been stacked more uniform in a parallel direction and not as randomly orientated as these individual crystals within these samples. The matrix also shows compacted specular hematite.

A quick flick through some literature ...

Brief description of the host granite.

"It is generally rather coarse, but in some parts fine grained, and consists of quartz, containing numerous liquid cavities, orthoclase, oligoclase and plagioclase felspar, dark-brown and black mica (muscovite and biotite) haematite, chlorite, calcite, perthite, apatite and tourmaline.
The felspar is more or less impregnated with haematite, which gives a reddish tint to the rock, and that tint is more apparent on a weathered surface than where it has been recently fractured, as the haematite, when liberated from the decomposed felspar, spreads over the whole face of the rock."

Postlethwaite, J. "Mines and Mining in the (English) Lake District" (1877; 3rd edition 1913)


"The granites and microgranites have been much altered. Micas are often partly replaced by reddish-brown hematite and feldspars often partly altered to scaly sericite."
"Faulting has occurred at several periods since the granite was intruded. Some faults acted as channels for mineralising fluids, especially those carrying hematite, during a major period of iron mineralisation probably in Cretaceous or Tertiary times."

Young. B. 2000. "Chapter 6. The Eskdale Granite, Lakeland Rocks and Lanscape - A Field Guide." Cumberland Geological Society.


"On the south side of the Esk some of the veins yielded a beautiful, stalactitic form of hematite ... (Smith, 1924).
"Black, glossy stalactitic masses, some associated with fawn dolomite, common locally."

"South Cumberland Mine, Eskdale (NY179000):
From the Gill Force Workings (Keswick Museum)
Compact specularite occurs on the dumps from No.6 Level on Gate Crag Vein."

Young, B. 1987. 'Glossary of the Minerals of the Lake District and adjoining areas." (Newcastle upon Tyne: British Geological Survey.)



Some more pictures ... sizes as stated before in Davids original post.

Any help on the way that these were formed will be much appreciated!

Cheers

Philip