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Identity HelpUnknown crystal from Afghanistan

22nd Feb 2019 18:01 UTCNick Gilly

Hi all.

I bought the following crystal as an unknown from one of the Peshawar sellers on eBay. It's apparently from Badakhshan Province, Afghanistan, maybe from the Deo-Darrah pegmatite? The crystal is 4.8 cm long, by 2.7 cm 1.7 cm. When I first saw the pics I wondered if it was topaz, but now I have the specimen here, it's clear it isn't. It has a 6-sided cross-section, is vertically striated and has cleavage planes showing in 2 directions I think. It feels quite dense, comparable to topaz, so the SG I would estimate to be around 3.5. It weighs 33 grams to the nearest whole number. The crystal shows some weak peach-coloured fluorescence using my cheap 395 nm UV torch. It scratches glass but needs a bit of pressure to make a clear scratch, so I'd estimate hardness to be around 6. It looks like it may crystallise in the monoclinic system. Here's some pics from the auction below:

[img]https://i.ebayimg.com/images/g/uYwAAOSwXyBcU0sY/s-l1600.jpg[/img]

[img]https://i.ebayimg.com/images/g/-08AAOSw3-9cU0re/s-l1600.jpg[/img]

[img]https://i.ebayimg.com/images/g/yBwAAOSwf0hcU0sm/s-l1600.jpg[/img]

[img]https://i.ebayimg.com/images/g/bVoAAOSwRKVcU0uK/s-l1600.jpg[/img]

[img]https://i.ebayimg.com/images/g/WxoAAOSwdgxcU0ur/s-l1600.jpg[/img]

[img]https://i.ebayimg.com/images/g/jmwAAOSwptZcU0u5/s-l1600.jpg[/img]

It's maybe not that clear from the images but the crystal has a pale yellowish-greenish tinge. It's a handsome specimen.

So, any suggestions most welcome.

Thanks

22nd Feb 2019 18:36 UTCFrank K. Mazdab 🌟 Manager

it reminds me of clinozoisite

22nd Feb 2019 19:23 UTCNick Gilly

Thanks Frank. It's a pale clinozoisite if that's what it is. I think the mystery mineral is slightly softer than clinozoisite actually.

From a couple of angles there is also a clear chatoyancy/schiller type effect, as if there are parallel fibres or very thin tubes reflecting the light internally. I don't know if this helps.

22nd Feb 2019 20:01 UTCFrank K. Mazdab 🌟 Manager

if you hadn't said it was from central Asia I would have originally guessed it was a poorly-colored tanzanite (=zoisite) from Merelani; I suppose zoisite is also a possibility, but as clinozoisite is already well-known from the region I went with the odds.

22nd Feb 2019 20:27 UTCJosé Zendrera 🌟 Manager

Except for some faces at termination it reminds me marialite.

Six sided section could be an octagonal section in which two faces are missing. Vertical striation, luster, color, interior fractures and yellow fluorescence under long wave (with a filtered 365 nm lamp) are in accord with marialite.

Nick, can you check fluorescence under short wave? it should be red in marialite from Badakhshan.

Also can check the angles between prism faces. If it's hexagonal you will find 120º. Marialite can have 135º and 90º

Top left: Halogen light

Top right: UVA

Bottom left: UVC

Bottom right: UVA + UVC

22nd Feb 2019 20:38 UTCNick Gilly

Thanks José. I only have the 395 nm torch so can't check SW UV.

Using a protractor the angles look close to 90º and 130º. I think it's slightly less than 90º and slightly more than 130º, so that may mean it's not tetragonal.

22nd Feb 2019 20:45 UTCErik Vercammen Expert

Spodumene?

22nd Feb 2019 21:49 UTCNick Gilly

Thanks Erik. Yes this has also been suggested on the Facebook group. It's certainly a good possibility, although that steep symmetrical termination is not a usual habit.

It probably is a pyroxene of some sort.

22nd Feb 2019 22:37 UTCNick Gilly

I found a completed auction from the same seller of another crystal of this material, and it shows the fluorescence: peach in LW UV, blue in SW UV:

https://www.ebay.co.uk/itm/228-CT-Florescent-Full-Terminated-Natural-Color-Unusual-Unknown-Huge-Crystal-AFG-/273599807983?hash=item3fb3d1c1ef%3Ag%3AE4QAAOSwSlpcCugd&nma=true&si=ixjQQNnReTNMiRRT05C3KlM5GqA%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557

Some more useful info that will hopefully help with an ID.

22nd Feb 2019 22:51 UTCScott Rider

I vote for yellow zoisite. Just curious, what did the seller claim it was?

This one is tricky, and could be a number of different minerals. But I was also thinking spodomene as well...

However, my very first gut feeling was it is richterite. Mostly because I was holding one the other day that has similar clarity, color and striations, but not the termination. I scoured a TON of images of that and have found none that have that termination. I can't seem to find a text book schematic of the mineral and am not too familiar with the mineral.

Whatever it is, sure is a good looking crystal with a decent termination... If it is a pyroxene, then that is a REALLY good sample.

https://www.minerals.net/Image/15/202/Zoisite.aspx

22nd Feb 2019 22:56 UTCNick Gilly

Hi Scott. The seller didn't know what it was, so it was listed as an unknown. I'm hoping that completed auction showing the LW and SW UV response will be a clue. I don't know of any spodumene that fluoresces blue in LW UV.

If it is richterite, then it's a damn good one! I'd be amazed if it was though. Probably something more mundane.

23rd Feb 2019 03:13 UTCIan Nicastro

Scapolite makes logical sense coming from that area, and Scapolite would be UV reactive.

23rd Feb 2019 04:26 UTCPaul Brandes 🌟 Manager

Based on the UV colours, I'd agree with Ian: Scapolite.

23rd Feb 2019 05:30 UTCFrank K. Mazdab 🌟 Manager

A photo looking directly straight down onto the pyramidal terminations and lit so the faces are somewhat reflective would be very useful. If the four pyramidal faces that constitute the form aren't at 90° to one another, it can't be scapolite. From the fourth photo that slightly reflects off the pyramidal faces, the two visible paired faces actually look like they're at an obtuse angle to each other, and so from above would probably appear as an obtuse angle between two rhomb faces rather than as a 90° angle between two faces of a square. A photo looking straight down would also give a better perspective of the angular relationships among the prism faces, and may shed some light on whether they're sets of rhombic prisms or sets of pinacoids (hence indicative of orthorhombic or monoclinic symmetry), or if the angular relationship could be consistent with two tetragonal prisms (although it's already problematic that in the fifth image, the E and W faces of a presumed tetragonal prism are missing). In lieu of a more definitive photo, my gut feeling remains with either zoisite or clinozoisite.

This "dilemma" could also easily be solved with a simple precise density measurement. Even to just one decimal place, marialite has a density of 2.5 to 2.6 g/cm³... all of the other choices that have been mentioned (richterite, spodumene, zoisite/clinozoisite) have densities between 3.1 and 3.4 g/cm³. A better cleavage determination would also be definitive to differentiate between scapolite, pyroxene, amphibole and the epidote group, but of course it's neither practical nor desirable to produce fresh cleavage surfaces on this particular nice crystal.

23rd Feb 2019 07:13 UTCDoug Daniels

Have to agree that the specimen shown is an ideal candidate for a decent specific gravity determination. Of course, whether Nick has a scale with enough accuracy, is another question (I know I myself don't have one....).

23rd Feb 2019 07:31 UTCFrank K. Mazdab 🌟 Manager

Nick clearly has access to eBay and the financial resources to buy cool minerals... if he doesn't already have a balance of sufficient sensitivity (to ±0.01 g should work) appropriate for density measurements, he can spend a few £ on one. And to be fair, the recommendation to buy basic inexpensive tools necessary to help identify minerals doesn't apply just to Nick, but indeed to everyone who's serious about ID-ing unknown minerals.

23rd Feb 2019 07:51 UTCNick Gilly

Thanks guys. I actually am a cheapskate when it comes to buying minerals lol. That crystal only cost $16.50 before shipping, so it didn't exactly break the bank.

I don't have an accurate balance to calculate SGs (the one in our kitchen only displays to the nearest whole gram) but for those suggesting a scapolite I can eliminate that possibility. The listed SG range for marialite-meonite is 2.5-2.78, so if it was a scapolite it would have the same sort of light feel as a quartz crystal. This specimen is definitely denser than that, and feels heavy, like a topaz. So I'm pretty sure it's not a scapolite.

Here's a really quick view of the termination from above, if it helps:

23rd Feb 2019 08:06 UTCFrank K. Mazdab 🌟 Manager

definitely not tetragonal... looks orthorhombic as the NE, SE, NW and SW faces are of similar size and appear to form a rhombic prism (and the N and S faces seem to be a pinacoid), but I can't rule out monoclinic from this view since the b-axis making a possible non-90° angle could be roughly perpendicular to the plane of the image and any deviation from 90° could also be very subtle ... I'm sticking with my previous guess... either zoisite or clinozoisite, and I'm starting to lean more towards zoisite. I suppose the next step will be either some optical measurements, or popping the whole crystal into an SEM set up in environmental mode (so not requiring any carbon coating) for a quick qualitative EDS check for critical elements.

This 200g balance (±0.01g) costs under $6... no one's bank will be broken:

https://www.ebay.com/itm/Portable-200g-x-0-01g-Mini-Digital-Scale-Jewelry-Pocket-Balance-Weight-Gram-LCD/302976550494?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D20131003132420%26meid%3Ddb7c8f7016d34680a6e22f48170b5004%26pid%3D100005%26rk%3D10%26rkt%3D12%26mehot%3Dag%26sd%3D332701401811%26itm%3D302976550494&_trksid=p2047675.c100005.m1851

23rd Feb 2019 08:57 UTCNick Gilly

Someone in the Facebook group has posted a pic of what is apparently a diopside crystal from Badakhshan Province and it looks like a dead ringer for my specimen. So, assuming his ID is correct, diopside is looking like the most likely candidate.

I'm still hoping to get further tests done on this specimen though as I would like a confirmed ID.

Edit: Frank thanks for the link to that balance. I didn't realise they could be bought that cheap!

23rd Feb 2019 09:46 UTCFrank K. Mazdab 🌟 Manager

diopside may be plausible... however, by that same token, you might want to also take a look at some of the Pakistani forsterite photos as well. Although most specimens are deeper green, a few photos show paler crystals and with similarly steep terminations. And the cross-section would also be consistent.

23rd Feb 2019 11:14 UTCNick Gilly

Thanks Frank. I doubt if it's forsterite. I see no photos of any specimens as pale as this one. I also have a thumbnail specimen of a terminated gem green forsterite crystal from Pakistan and it looks completely different, including the cross-section.

I'm going with diopside for now.

24th Feb 2019 21:36 UTCMichael Christensen

Peridot was my first thought when I saw it. That pale is rare, but it definitely does happen. I'd put the largest I've seen around 2-3cm. I'd say sometimes you don't notice the Talc is gone, but it's more like I'm too busy celebrating the Talc being gone to notice the prize wasn't what I'd hoped. :)

25th Feb 2019 07:28 UTCIan Nicastro

Diopside makes sense from that deposit.

25th Feb 2019 15:17 UTCNick Gilly

Thanks again guys. It's still a weird shape for diopside with that steep termination.

There's a mineral show this coming weekend which always has some dealers from Afghanistan or Pakistan. I'll be taking this crystal with me, as well as the suspected bastnäsite specimen. I know they've also had people there with testing equipment in the past, so someone may be able to held ID them.

25th Feb 2019 17:41 UTCFrank K. Mazdab 🌟 Manager

I wonder if the crystal will end up turning out to be topaz after all...

25th Feb 2019 19:40 UTCNick Gilly

No it's definitely not topaz. Wrong shape and not hard enough.

26th Feb 2019 01:21 UTCFrank K. Mazdab 🌟 Manager

don't be so quick to dismiss that. Actually, the shape isn't wrong at all (the cross section in your final photo would be consistent with orthorhombic symmetry: a rhombic prism with an additional pinacoid; and the termination in your fourth photo would be consistent with two rhombic pyramids). The extra (100) or (010) pinacoid in the cross section may not be a common form for topaz, but it's not crystallographically disallowed.

As for hardness, that's a test that's frequently not done well (works best with a set of hardness test points, which few people use)... in any case, you noted it scratched glass but didn't mention whether it also scratched quartz or if quartz scratches it (on the discreet base), even if some good amount of pressure is needed. Your fifth photo seems to show the classic basal cleavage, and your density estimate (admittedly also a test not often done well, especially when done by just 'heft" and not quantitatively) is self-described as consistent with topaz.

It will be interesting to hear what the dealers at your upcoming local mineral show think about this crystal, as well as subsequently when you're able to obtain some near-term quantitative density data (after you buy a $6 scale) and any possible future chemical or optical data you're able to get.

26th Feb 2019 08:59 UTCNick Gilly

Thanks Frank.

It doesn't scratch quartz, so my hardness estimate of 6 stands. It also appears to show cleavage planes in 2 directions. So for me, that rules out topaz.

26th Feb 2019 20:02 UTCIan Nicastro

I've been thinking more about this piece, I am convinced it's either Diopside or Scapolite, it just has a weird atypical termination, as both of those minerals are well reported from this deposit and fit the hardness. The fact you are getting some UV response leans me toward Scapolite, but I can't tell if the piece is pale yellowish or pale greenish from the white balance of your photos. But as was said above... SG is the best way to ID this, as those two minerals have quite different SGs, and I wouldn't just trust someone's visual opinion from a club. Richterite is ruled out because it tends to be very thin. I strongly disagree with Peridot & Clinozoisite.

26th Feb 2019 20:04 UTCNick Gilly

It's too dense for scapolite Ian. I can tell that just from its heft when picking it up. As for the colour, it's a pale yellowish-green. So far, I'd say that diopside is the most likely candidate, albeit a weirdly-terminated example.

26th Feb 2019 20:47 UTCFrank K. Mazdab 🌟 Manager

regardless of what UV response it gives, the final cross-section photo, albeit a bit blurry on some of the crystal edges, shows the crystal is clearly not tetragonal; hence it can't be scapolite. The crystal appears orthorhombic but could also possibly be monoclinic as well, so barring some markedly uneven growth, the eventual identity is almost certainly going to fall into one of those two crystal systems. I know when students start learning mineralogy they always bitch and moan about the first two-week crystallography component of class, and inevitably lament, "why do we have to learn this... you never see crystals as nice as the lab specimens in real life?" Well, this is why...

And as an aside, several posters have noted, "is consistent with the locality". What locality? Nick said "apparently from Badakhshan province". Badakhshan not a deposit... it's a region of 44,000 km² (that's about the size of Switzerland, and probably as geologically diverse). Half the minerals in mindat are likely consistent with that locality. As for "maybe from Deo-Darrah pegmatite"... did the seller say "maybe from" or is Nick saying "maybe from"? In either case, "maybe from" only muddies the waters and should not have been included as a clue. Because I bet if the clue were instead, "maybe from Tanzania", there would have been an entirely different set of guesses. Either the specimen "is from ___________" (then a good clue to it's identity because then its geology can be incorporated), or one has an unknown mineral from an unknown locality, and the more fake clues that are added don't help in solving either mystery.

Take it to the nearest university and have a professional examine it live, or better yet, break a tiny chip off the bottom where it can be discreetly done and have it SEMed or X-rayed... then let's put this thread to rest.

28th Feb 2019 07:49 UTCIan Nicastro

Sorry, I was under the impression this piece was likely from the Koksha Valley area, but you're totally right that it could also be from the pegs in Deo Darrah. I've had a fair bit of Clinozoisite tested for a friend in Peshawar, and I've been shown a lot of different colors and shapes of Clinozoisite & Zoisite from Pakistan & Afghanistan, that's why I felt this wasn't Clinozoisite. I thought of a couple species we didn't bring up yet... Tremolite, although usually the crystals don't have good terminations from that region. One other option... Herderite... might that explain the weird twinning appearance on the termination? Some Hydroxyl-herderites look somewhat similar to Topaz at first glance.

28th Feb 2019 09:36 UTCJohan Kjellman Expert

what is the angle between the two cleavage directions? I guess one is the horizontal plane...

the crystal looks similar to pyroxene (aegirine) crystals depicted in Goldschmidt, vol 7, for example plate 44, fig 18

cheers

28th Feb 2019 10:09 UTCFrank K. Mazdab 🌟 Manager

Hi Ian,

I think you mis-read what I wrote about the locality. The only thing known (or believed) about the locality is, to quote what Nick originally wrote, "...apparently from Badakhshan Province, Afghanistan, maybe from the Deo-Darrah pegmatite?" It's not clear whether that assessment is Nick's or the dealer's, but because of the qualifiers of both "apparently" and "maybe", those purported localities unfortunately don't help in identifying the mineral... rather, because the true locality isn't actually known, those purported localities only serve to prejudice us into making assumptions about what the mineral could be (because we include or eliminate possibilities based on what we understand of the geology of these places) but that may or may not be true. All we know about the locality, with reasonable but not absolute certainty, is that since the dealer is from Pakistan, the sample is probably from somewhere within a few hundred miles of his home base (which cover 2-3 countries). Unless the dealer offered more concrete information on his listing (I don't know... I didn't see the listing), that really is all we know; so, the dealer didn't acquire it in Africa or South America (probably... lol).

In any case, your suggestions of tremolite and/or herderite are both consistent with the apparent crystallography (indeed, as herderite can appear pseudo-orthorhombic, it's probably even one of the better guesses), and both would seem consistent with some of the other properties as well. So those two additional suggestions can be piled on to the now fairly extensive list of potential identities that include everything but the kitchen sink (but not scapolite [lol], or anything else isometric, tetragonal, hexagonal or trigonal; or anything metallic; or anything one can scratch with their fingernail). Ultimately, when it comes to identifying minerals from a photo, even the most professional of us (including me) are relegated to being just handicapped arm-chair mineralogists. We might offer some good guesses... one or several of us might even end up correct. But ultimately there's no substitute for a professional examining the crystal live in his or her own hands. We can all guess in perpetuity, but in the end we're going to have to wait for Nick's report back from someone at a local museum or university.

28th Feb 2019 10:20 UTCFrank K. Mazdab 🌟 Manager

Hi Johan,

If the horizontal plane is a cleavage direction (and from the fifth photo it seems that way to me too), then it can't be a pyroxene because the two cleavages in pyroxene are {110} and intersect in the a-b plane, and so would be parallel rather than perpendicular to the long c direction of the crystal (this orientation would be true of amphibole too). However, if the horizontal plane actually isn't a cleavage, then pyroxenes or amphiboles are back on the table.

28th Feb 2019 12:21 UTCPeter Slootweg 🌟

I have to agree with Erik that spodumene is very likely. Shape, color, cleavages en LWUV response (peach color) match very well. Deo Darrah is known for its pale yellow spodumene. The odd termination may be due to twinning so typical for spodumene. Photo's 1, 2 and 4 show a deep groove on the front facing prism face that ends at the mirror plane of the termination, and looks like a twin boundary to me. Diopside remains an option. If it's a diopside from a marble enviroment the little black spots are usually tiny corroded pyrite crystals. These would rule out spodumene.

28th Feb 2019 13:35 UTCNick Gilly

Hi again.

The location was just listed as Badakhshan Province, nothing more specific than that. A lot of the specimens listed from there seem to be from the Koksha Valley, and this specimen looked different to most I've seen from there, so the Deo Darrah pegmatite was a guess. I've seen quite a bit of diopside listed from the Koksha Valley (some of them as unknowns too) and these have been bright green, sometimes with lazulite spotting the crystal, making for a nice colour contrast. This specimen is obviously very different in appearance.

The cleavages seem to be in two directions, the horizontal ones slightly offset in both directions from the base, and the vertical one does seem to be directly parallel to the c axis.

The UV response seems to be peach in LW UV, and blue in SW UV (judging from the pics in the other auction). I don't know of any spodumene that fluoresces blue in SW UV, but I could be wrong.

It does look a bit like some specimens of hydroxylherderite I've seen, but I do have a crystal of this material from Brazil, and that doesn't scratch glass. This specimen does.

If it is spodumene it's got a very odd termination.

I'll be taking it to the Kempton Park Rock & Gem Show at the weekend, so maybe we'll get a better idea from some of the dealers there. If not, then I may see if I can get Southampton University to do some Raman spectroscopy on it.

28th Feb 2019 17:37 UTCFrank K. Mazdab 🌟 Manager

Hi again Nick,

since the dealer you bought it from didn't know what it was, it's possible the dealers at the mineral show also won't know (or might also disagree with each other). While it's still probably a worthwhile endeavor to give the dealers at the mineral show a try, if you indeed do know someone at Southampton that can do more sophisticated testing for you, I'd definitely recommend that. The latter option might be especially useful if the mineral turns out to be either very unusual, or it's a member of a series/family (like herderite/hydoxylherderite) where the individual members couldn't be easily distinguished by physical means alone.

28th Feb 2019 17:50 UTCNick Gilly

Actually re-reading Peter Slootweg's musing about a twin boundary, he could be on to something there. It does coincide with a mirror plane at the termination where the two diamond/lozenge shapes at the top are bisected. So maybe it is spodumene if that is the case. If it is then it's the most complete and symmetrical termination I've ever seen in this mineral. Normally they are simpler and very lop-sided, as well as partially etched.

I will phone Southampton University tomorrow and see if I can get someone there to test it.

1st Mar 2019 17:01 UTCNick Gilly

I've just spoken to someone from the Advanced Composite Materials Facility at Southampton University, and he says that yes, I could come over with the crystal and he should be able to run it through their Raman spectrometer. I'm hoping to go there next week. If so, I'll scan in the results and post them here. I'm sure this should give us a positive ID.

1st Mar 2019 19:39 UTCFrank K. Mazdab 🌟 Manager

Hi Nick,

Although it's possible they may send you home with an actual spectrum that you can upload and post here, it's more likely that their instrument connects to a database of Raman spectra (perhaps even the RRUFF database) that compares the spectrum to what's in their database, much like how powder XRD matching is done, and looks for matches.

So it will output a list of potential mineral (and perhaps chemical compound) matches, in order of decreasing probability. You'll want to post the list of the top several matches. As Raman spectra are directional, you (or the instrument technician) might also want to measure the crystals in two or all three principal orientations, if possible, and include those results here too. Then we as the arm-chair mineralogists can consider the minerals on your list(s) in the context of the other properties already posted here (crystallography, hardness, density, color, "locality") to ascertain which of the list entries is most plausible (and while the best answer typically is one of the minerals at the top or close to the top of the list, that's not always guaranteed).

Although posting the actual raw spectrum here might be interesting, few if any of us here have our own Raman databases handy and so we probably wouldn't be able to offer much ID help from the raw data itself. But for those well-versed in Raman spectroscopy, looking at the finer features of the spectrum could offer an entertaining diversion.

1st Mar 2019 22:31 UTCNick Gilly

Thanks Frank.

It looks like it may have to be the week after next now, but fingers crossed. Before then, I'll see what transpires at tomorrow's Rock & Gem Show.

1st Mar 2019 22:35 UTCFrank K. Mazdab 🌟 Manager

no worries... we're not going anywhere. And your crystal is probably a few million years old, so it too can wait another couple of weeks for its secrets to be revealed.

2nd Mar 2019 16:39 UTCNick Gilly

Well, it's a mixed bag after showing the crystal to several dealers. A couple of Pakistani dealers had no idea what it was but two suggested spodumene, and one seemed pretty certain. One of the UK dealers doesn't think it is spodumene because of the crystal shape.

I think spodumene is looking likely though. I'll find out for sure when I have it tested at Southampton University.

As an aside, I actually spent very little money at the show but did see one dealer with a parcel of gem rough pink spinel from Tajikistan. I picked out two pieces showing some crystal faces, at the really cheap price of £1/gram, and then a couple more later, by which time the dealer had raised the price to £3/gram lol. Still, 4 small gem partial crystals at a total of £7 is a steal!

20th Mar 2019 18:13 UTCNick Gilly

OK, Raman spectrometer results are in and the answer is...

...diopside!

20th Mar 2019 18:36 UTCScott Rider

Wow, sometimes visual IDs can be spot on!!! (going off your facebook comment). It is a really cool diopside crystal you got there Nick!! Decent size, really nice termination. The diopside I can find from Calumet mine have a basal pinacoid termination much different than your specimen, if you are lucky to find one that isn't altered to actinolite.

20th Mar 2019 18:56 UTCFrank K. Mazdab 🌟 Manager

cool... good that the mystery is finally solved.

But a couple of other noteworthy outcomes then are (1) that those horizontal surfaces in several photos that look like a basal cleavage are simply fractures; the well-known near 90° {110} cleavage in pyroxene would be parallel to the length of your crystal. And (2) your crystal isn't from a pegmatite... at least not from any granite pegmatite that would abundant in the region.

20th Mar 2019 18:57 UTCNick Gilly

Thanks guys. It's presumably from a skarn, like the dravite specimen that was confused with bastnäsite.

It's certainly an odd termination for a diopside.

20th Mar 2019 19:49 UTCFrank K. Mazdab 🌟 Manager

This one probably not from a skarn (too pale... insufficient Fe) but simply from a marble... your dravite perhaps from a skarn or other carbonate-bearing protolith, but keep in mind that any tourmaline with a "Y-site" filling of even (Mg_1.51Fe²⁺_1.49) is still technically a dravite (assuming the other sites are filled appropriately) and such mixed Mg-Fe compositions occur in a wide variety of rocks. Put a drop of acid on the matrix material you first thought was calcite and then thought might be feldspar... it may indeed still be feldspar. If there's no carbonate in that pale-colored matrix, I suppose endoskarn can't be ruled out, but I'd then be open-minded to more diverse origins.

20th Mar 2019 20:57 UTCIan Nicastro

Awesome you got this verified as well, I really had a feeling Diopside was going to be one of the main contenders from everything we brought up.

20th Mar 2019 21:30 UTCNick Gilly

Thanks again.

I think the matrix for the dravite may be feldspar with some calcite as well as the mica. This is based on the fact that quite a few bits scratch glass but there is also a softer mineral intermixed that doesn't. For example there are some crystals adjacent to the dravite that look like they show calcite cleavage faces.

21st Mar 2019 01:25 UTCPaul Brandes 🌟 Manager

Looking at the specimen and the UV response, I would have never thought diopside.

Thanks for keeping us in the loop throughout, Nick!

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