FMF - Friends of Minerals Forum, discussion and message board

[bugrock]

Hello,

I am looking for information on orbicular hematite from Keswick, Cumbria, UK.
Specifically what is the composition of the material and how did it form? Is the specific location known, from a mine or a quarry?

Thanks,

George

[colin robinson]

I live in north Cumbria, not far from Keswick and have been field collecting in the area for the best part of fifty years. I have to say I've never seen or even heard of this material. It looks rather like orbicular jasper, a type of rock rather than a mineral. It also looks like it contains a lot more than just hematite.

There is a Birkett Bank near Keswick but the local geology would really preclude its being from there.

A quick google brings up several images from the same source. Perhaps you could ask the person you acquired it from for more information.

[bugrock]

Colin,

Thanks for your reply. I agree the material appears to be a "rock" stained with or containing hematite grains but certainly not a habit of the mineral hematite. There is an example out there for sale but the seller has no knowledge, it was found in an old collection. Also, there is an example posted on mindat but the matrix is darker and perhaps of a different composition. Still, it has the zoned orbicular look.

Perhaps someone can offer additional information.

George

[ian jones]

In many years of collecting British minerals, I have never seen anything remotely similar from Cumbria (or elsewhere). Can't even suggest a possible UK location, perhaps someone else may be able to though.

[Philip G]

Hi all,

Like Colin and Ian, i havent seen any specimens resembling this material but it is certainly interesting. The unusual presence of a minor locality name in Birkett (or Birket) might tentatively add a little validity to its claim of origin though.

Looking at the 1:50000 geological map of the area, next to a microgranite exposure and its quarry workings at Birkett Bank, there is an outcrop of the Birker Fell Formation which is described as 'plagioclase-phyric andesite lavas and subordinate sills, some pyroxene-phyric basaltic andesite and dacite lavas, and with interbeds of tuff, lapilli tuff, pyroclastic breccia, volcaniclastic sandstone, conglomerate and breccia.'

I'm certainly not stating this as the likely origin of the specimens in question but thought i would share the map information just in case it serves to trigger further discussion. It would be interesting to know the actual rock type (as opposed to 'orbicular hematite') and the date of collection if given on the original labels.

Phil

[Philip G]

Just to follow on with this. I have gone back into the geology texts and the following descriptive extract describes Birker Fell Formation (BFA) outcrops on the opposite side of St Johns beck between High and Low Rigg but still in relatively close proximity to the quarry workings and BFA outcrops mentioned in the previous message.

'Retracing one's steps to the bottom of the crags, an interesting volcanic succession can be examined at leisure. The lowest exposures (in the lowest crag) are red breccias (fragmental deposits) which are believed to be flow-brecciated andesite or basaltic-andesite lava. The red iron oxide colour suggests that subaerial weathering occurred shortly after eruption. Bedded tuff forms the bench above this lava and rests uncomformably upon it, indicating a considerable pause in volcanic activity.'
F Moseley (1983). The Volcanic Rocks of the Lake District. London and Basingstoke: The MacMillan Press LTD. P.48.

Of interest in this passage is the mention of the subaerial weathering and the red iron oxides in locally adjacent (to Birkett Bank) rocks of the same formation. Were dacite/rhyolite lavas weathered in the same way and were some of these showing orbicular patternation?

Anyway, we will probably never know unless they are relocated in the field or unless actual accurate provenance and identification for the specimens is shown. So for the time being it is unlikely to matter a great deal to anyone but the vendor or buyer but i still find it of potential interest in a local-to-my-area kind of way.

Phil

[bugrock]

Thanks for the comments.

I have a contact at Harvard Museum and will ask if there is additional label or catalog information. Also, perhaps the date of acquisition is known if not the date of collection.

Will post another message if I learn more.

George

[Roy Starkey]

Hi Everyone

As previous contributors have noted, I have never seen anything like this from the Lake District, never mind Keswick. The local geology is very unlikely to have produced a specimen of this type.

I have consulted a friend of mine who was formerly the District Geologist for Northern England (this was his "patch"), and he has not seen anything like it before from Cumbria.

It is conceivable that the "Birket" (should probably be Birkett) may refer the the mineral dealer John Birkett (ca.1836-ca.1897) (see the Mineralogical Record Label Archive and Mick Cooper's book - "Robbing the Sparry Garniture"), as he was based in Keswick.

It would be helpful to know if the mineral is actually hematite - suggest you ask Harvard if their specimen has been analysed. The specimen certainly has generated a fair bit of interest!

Regards

Roy

[bugrock]

Discussion on this topic can also be found on mindat (simply search on the term "keswick" to find it).

There are images of purchased specimen there.

If anyone has knowledge of the likely locality still interested in learning more.

George