[Closed] mineraltrackworld

looks like quartz with iron staining.

did you try scratching it with a knife? The host rock looks a bit like a limestone so it may well be calcite. If it is igneous though then it is more likely quartz as mentioned.

Location would identify the host rock and would narrow it down nicely 🙂

@welshfarmer - The hill was once quarried for limestone. You can see the remains of the quarry on this video. It was also used a hillfort.

Foel Formation (FOF)NamePreviously referred to as the Lower Brown Limestone (Strahan, 1890), the unit was subsequently renamed the Foel Formation by Warren et al. (1984).Type sectionNorthern of two quarries on western side of Moel Hiraddug at Tan-y-Foel [SJ 0607 7834]: section through the upper 12.9m of the formation (Warren et al., 1984).LithologyHeterolith of dark grey peloidal limestones, shelly, oncolitic and locally ooilitic limestones, porcellanous limestones, and fossil plant-bearing calcareous siltstones and calcareous sandstones. The limestones are locally dolomitised.Lower and upper boundariesLocally, limestone of the Foel Formation conformably overlies reddened ‘Basement Beds’ (Ffernant or Penbedw formations), but elsewhere rests unconformably on Silurian rocks of the Clwydian Range (Nantglyn Flags and Elwy formations).The top of the formation is a conformable contact with thicker bedded limestones of the Llanarmon Limestone Formation.ThicknessUp to 88 m in thickness, apparently thinning and dying out southwards.DistributionConfined to the north and east of the Clwydian Range in north-east Wales, between Moel Hirradug

The surface of the crystals looks waxy so my quess is calcite. Take some acid next time and if it fizzes it's calcite.

if it fizzes it’s calcite.

Or dolomite ..

Local lead mining also suggests a high degree of hydrothermal alteration so it could be lots of things... even quarts as "peloidal limestones, shelly, oncolitic and locally ooilitic limestones" are likely silica cores.. a little like the chalk where the diatoms dissolve and then you get flint/cherty bands and nodules except the local mining of lead would probably indicate hot water (hydrothermal)..

Dolomite crystals don't fizz.

Yep, looks like some kind of hydrothermal breccia with coarse carbonate crystals, most likely calcite, with hematite staining (red).

Any metallic-looking bits in there?

Dolomite will generate CO2 with HCl if it has been pulverised.

Or if it's heated up. I'm just suggesting a simple field test to complement Welshfarmer's suggestion of scratching with a knife. Fell free to add more simple tests.

All this reminds me me of geological folklore in which a mountain in Scotland was first mapped as quartzite but later geologists found it to be Barite which is quite useful stuff.

When you lick it does it make you chakras go all tingly?

Take some acid next time

Last time I took such advice it turned out that the cave I was sleeping in had not just a sandstone roof but something more akin to an infintely-patterned Moroccan rug whose organic designs moved and shifted like slow, crystalline cosmic winds.

After some time, Puckish faces emerged from the patterns to inform us that we were in fact attempting to sleep in the bonafide den of a pack of spectral hunt-hounds who were barking distantly, announcing their return.

Would vinegar work?

Would vinegar work?

I've tried it on my chips, the cave roof remained staunchly cavelike.

Unobtainium?

Would vinegar work?

No, but the hydrochloric acid you can get in DIY stores would be strong enough. If you can't get acid try mushrooms, there's a good chance you'll find some on that hill.

Dolomite crystals don’t fizz.

Dolomite will generate CO2 with HCl if it has been pulverised.

or with 25% HCl
or quartz (or indeed most things not PTFE) will fizz nicely with HF though you probably don't want to carry that about... I did spend a whole summer dissolving various basalts in HF for ICP AES...

Dolomite crystals don’t fizz.

Whatever .... no point arguing and actually posting facts as it would take more than 20 qwords

Calcite, pyrites and galena

Would vinegar work?

Some strong acetic would but it won't tell you if its calcite as there are obviously non Ca metals which is what makes it interesting... .. most of which will still react to strong acetic or weak (10%) HCl

Unless you find some very pure calcite which is cool as it strongly polarises light.
You can do cool stuff laid in a cave or like the Vikings use it to find the sun behind clouds...

The crystal symmetry is an easy one and based on your photo (though not super clear) they do not appear to be calcite using the crystal structure .. (there is high and low Mg Calcite both are defined by keeping the crystal structure of calcite) Once that is lost they are classed as dolomite ... but it looks like yours is way more interesting and has more exotic hydrothermal alteration. (Which isn't staining its a recrystallisation)

It could have Zn, Pb Fe2+ based on the local geology.. (very probably some Fe2+ due to the colour)

As ever, STW doesn’t fail to get into the gritty!

I think this is the last batch of usable pics I took (without going back to the SD card) but already loads of info thanks all

Those two do look more like altered calcite...at least in the bigger crystals and you can see the staining but between these is the more interesting (inorganic geochemistry wise) bits.

Look at this as what was left over in a supersaturated solution after the Ca was depleted... so you can get all sorts precipitating out as the PVT reaches the eutectic. This then leavers a new supersaturated mixture... etc. etc.

Those two images make it relatively clear that it's not quartz, it's calcite. You can see the wonky cleavage planes.

@stevextc you can see the differential weathering in places, where there is some remnant crystalline structure, but the transition into where inclusions (maybe be physical and chemical, I can't tell Fromm that) have interfered with the crystal growth and allowed the material to me weathered away in small pockets.
nice.

Meh.. I opened this thread expecting a long winded discussion about Shimano brake oil substitutes.

I thought it was a thread about being brave...