FMF - Friends of Minerals Forum, discussion and message board

[AndyH]

I'm looking at samples from (mindat location https://www.mindat.org/loc-4994.html ) Old Towns Quarry, an historic source of dolomitised/ magnesian limestone. It is now long closed and more recently become notable for its unusual reticulated form of fluorite. The quarry lies to the east of the edge of the North Pennines ore field in the North of England so the other minerals typically associated with the limestone and fluorite from that general area are unsurprising, e.g. calcite, barite, pyrite, sphalerite, and they are usually fairly readily recognised by eyeball inspection of the crystal form(s). In these samples, however, there are some crystal forms that are new to me that I'm having difficulty identifying 'just by looking'. I've looked at a very wide range of images and sources online to no avail, searching for examples of the same form (to at least identify the crystal system) and for examples of single / twinned crystal forms of likely candidate minerals e.g. metal sulphides. These are very small crystals (1 mm scale) and very minor components of the assemblages in the samples, so it's not possible to do hardness testing for example. But they are there, seemingly distinct of form and colour, so what are they? Suggestions welcome, especially if you can point me to an image of the suggestion matching the form displayed... Thanks in anticipation... [two images attached showing three crystals / crystal groupings]

[James Catmur]

Pyrite is listed for the locality?

[Sante Celiberti]

Arsenopyrite,

Take a look, on Mindat, at 2nd picture of Arsenopyrite from Monte Arsiccio (Tuscany).

[AndyH]

thanks - that does look like a very good match and appropriate for the location :-)

[AndyH]

[AndyH]