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Identity HelpCCC Prospect unknown

17th Jul 2019 20:51 UTCJacob Zonderman

Collected these the other day in some fresh pegmatite, there are at least 3 complete xtls and maybe 8 or so broken ones. Sure look like Microlite to me, but MinDat doesn't have it listed as a species found there (other option would be Zircon but to my knowledge most of them are var. Cyrtolite which I have some of from Hall/State Forest area that I found over a decade ago and they do not look like these guys). Best I could do for the photos at the time, it was hard to get a good shot showing the pyramidal shape from above. The loose xtl is photographed from the top and side. Included is a photo of one of the broken xtls to show some stepping on one of the faces. The photos show a lot of brown, but there is some olive shading when looking at it under a hand lens. I figure it might be worth getting it checked out to confirm what it is.

Loose xtl is 4mm across and the largest in matrix is 5mm across.

I found one at Hewitt just down the road a couple years back, that one is slightly bigger at 8mm across and 5mm tall.



17th Jul 2019 21:00 UTCJacob Zonderman



17th Jul 2019 21:09 UTCLouis Zulli

When viewed from the top, what shape do you see? A perfect square, with 90 degree angles? Or something else? Hard (for me) to tell from the second image.

17th Jul 2019 21:29 UTCRobert Nowakowski

They look like zircons to me.

17th Jul 2019 21:43 UTCTed Hadley


17th Jul 2019 22:38 UTCJacob Zonderman

Viewed from the top the one in matrix has 4 equal sides (with an attached sidecar) as does the loose one which has a contact on the side; there are also some more square bottoms of some of the broken ones. Either way neither Microlite or Zircon are listed as being found at the CCC.

17th Jul 2019 23:04 UTCRichard Gunter Expert

If it is a zircon it might fluoresce bright orange in SW UV. Microlite is unlikely to do that.

17th Jul 2019 23:11 UTCLouis Zulli

Aren't those pegmatites 400 Ma old? If so, that's especially nice-looking zircon. I'd expect much more metamict specimens.

17th Jul 2019 23:15 UTCRichard Gunter Expert

Hi Louis:

Metamict zircons are a function of the U+Th contents, not their age. Many of the Grenville Province pegmatites have metamict U-bearing zircons in them while the similarly aged phlogopite-apatite deposits have non-metamict U-free zircons.

17th Jul 2019 23:39 UTCLouis Zulli

Yes, of course. I am unfamiliar with the geochemistry of those pegmatites. I simply noted the presence of uranium and thorium minerals in the list for Haddam, and made an assumption, perhaps mistaken.

18th Jul 2019 00:43 UTCJacob Zonderman

Tested an found no fluorescence

18th Jul 2019 00:55 UTCLouis Zulli

Jacob Zonderman Wrote:


> Tested an found no fluorescence

Do you have access to a Geiger counter?

18th Jul 2019 00:58 UTCJacob Zonderman

I do have a digital one, though it's not with me at the moment.

18th Jul 2019 01:16 UTCLouis Zulli

Jacob Zonderman Wrote:


> I do have a digital one, though it's not with me

> at the moment.

A good specific gravity measurement from one of the detached crystals would be helpful too.

18th Jul 2019 01:21 UTCJacob Zonderman

I'll get on that as well. Thanks.

18th Jul 2019 01:54 UTCMichael Hatskel

Looks like Microlite to me.

Not listed for the locality -- so what?

18th Jul 2019 02:30 UTCJacob Zonderman

Michael, the site has been collected since the 17th/18th centuries and there are no references in old literature or from the past few decades when specimen collecting started back up so it's an interesting situation.

18th Jul 2019 02:51 UTCFrank K. Mazdab Manager

looks a bit more like zircon to me... in the top photo, it even looks like there are some weakly developed prism faces at the base of the pyramidal faces, although as the crystal appears embedded in some white-tack stuff almost to its equator, it's tough to really tell what's below those upper faces (and unfortunately, the second photo is out of focus).

18th Jul 2019 04:15 UTCMichael Hatskel

Hi Jacob,

Microlite is often associated with Columbite. In fact, such association is present in other pegmatites in the Haddam area. So why not here as well?

The second photo, although not totally in focus, looks very much like a side view of a typical distorted octahedron so often observed in Microlites.

From my experience with Virginia pegmatites, Zircons in granite pegmatite tend to be prismatic. Bipyramidal Zircons are more typical for alkaline rocks.

Most probable reasons for missing Microlite in the past:

- It is really rare here.

- Everyone was so focused on large Columbites and Beryls that tiny Microlites were simply "not in focus" and escaped collectors.

I admit I have not seen any literature about this locality. The writeup on the location page mentions that it is clearly Columbite-(Fe), with high dominance of Fe over Mn. Is it known where that Columbite falls in the Columbite-Tantalite series? There are Columbites that are barely across the 50/50 line, so very enriched in Ta. If that happens to be the case, the presence of Microlite can be further justified from the chemical stanpoint.

I look forward to see your SD results -- the SD shall be quite conclusive.

18th Jul 2019 08:31 UTCUwe Kolitsch Manager

Zircon or xenotime.

18th Jul 2019 08:33 UTCAlfredo Petrov Manager

I see only 11 confirmed species listed for that locality. That‘s quite meager for a Be,Nb,U bearing pegmatite, so I suspect that there are several more species waiting to be confirmed from there in future. Keep in mind that for the vast majority of localities the Mindat species list is incomplete, so "not on the list" is not a good reason to doubt something‘s existence.

18th Jul 2019 10:56 UTCJohan Kjellman Expert

agree - xenotime or zircon are most likely - statistics talks for zircon, but morphology in peg environment for xenotime.

there is also a third possible mineral - obviously observed in Haddam pegs - thorite


18th Jul 2019 13:25 UTCHarold Moritz Expert

CCC prospect is a very simple pegmatite, and has been heavily collected over the last few decades. The productive zone is only about 1 m wide, so very unlikely something new will be found here. But these are good finds I have not seen documented from there before.

There are many, many pegmatites in the area with columbite but no microlite. Microlite is present locally only at the handful of most evolved pegmatites, with plenty of Ta and Li and aplite and/or cleavelandite zones. There are zillions of microlites at the nearby Hewitt Gem Quarry, which has those characteristics, and similar Gillette, Swanson, Strickland, Walden, Hollister, Simpson and White Rocks Quarries, but that's about it. Pegmatites near these complex ones don't show any microlites and the Smith Quarry near this prospect is boring as hell, with really just schorl as a common accessory. Zircon is ubiquitous in all pegs, though, in small crystals, often clustered in the matrix. Xenotime is another possibility here, but difficult to ID from other similar-looking minerals without analysis and likely under-reported everywhere. The somewhat wedge shape to these photographed crystals and their color also suggests monazite, another good possibility.

The first columbite analysis definitely from here was written in Hunt 1852 (Hatch's crystal described in 1802 may be from here as I summarized in the locality description). Here are Hunt's wet chemistry results:

"Metallic acid, 80.60

Protoxyd of iron, 15.57

“ of manganese, 3.25

Lime, .50

Oxyd of tin, a trace


The composition is identical with that of the Bavarian and Middletown columbites; like the latter, the Haddam specimens appear to contain principally niobic acid."

Clearly Fe-dominant. The "metallic acid" is a mix of Nb and Ta oxide, but he gives an SG of 5.85, deep in the columbite range. I've had a few tested via EDS with similar results.

But from experience at other pegs around here, even where microlite is common, most col-tan is still columbite. I am finding that tantalite is Conn. is quite rare (working on writing up results from measuring the SG of dozens of Conn col-tans - 6 columbite SGs from CCC Prospect I've measured are 5.46, 5.62, 5.71, 5.95, 6.06, 6.15). Even where Ta is relatively abundant (see pegs listed above) the Nb seems to go into columbite while the Ta goes into microlite (and in a few places where Sn is abundant, into wodginite, too). Pyrochlore is almost completely undocumented in Conn. but analyses are few.

Anyway, careful SG of the loose crystals will help with their ID. I can get this done for you if you want. I will be at the multi-club picnic on July 28, bring them if you are attending.

18th Jul 2019 16:38 UTCSteve Hardinger Expert

The lack of a species listed here on Mindat shouldn't be used for determination of mineral species. For example, (until a few months ago) zircon wasn't listed for Elizabeth R Mine, Palal District, San Diego County, California. However working through some old self collected material from that locality sure enough...I found a crystal that was undoubtedly a zircon.

20th Oct 2019 03:37 UTCHarold Moritz Expert

EDS results are in! Drum roll's xenotime-(Y)! Peter Cristofono writes in his email to me:
We analyzed two spots (JZ01) and (JZ01B). They are both good matches for xenotime-(Y). JZ01 shows a trace amount of uranium, and a minor amount of dysprosium (Dy) replacing yttrium. These elements are not uncommon impurities in xenotime. The JZ01B plot also indicates trace uranium, but it's unlabeled.The trace iridium (Ir) shown in JZ01 is doubtful, so you can ignore it.

I'll post the spectra in a day or two; busy.

20th Oct 2019 06:34 UTCFrank K. Mazdab Manager

Thanks for reporting back on the results.

Oftentimes ID queries for compelling specimens are sought here, specimens that spark lively debate, but then we frequently never find out what they turned out to be.

It's nice to get "unknown specimen closure" this time. The zircon/xenotime/thorite crowd get their day today (especially those who specifically picked xenotime); the microlite crowd will get their turn another day, on some other pegmatite accessory crystal offered here for ID.

21st Oct 2019 13:59 UTCHarold Moritz Expert


21st Oct 2019 14:13 UTCHarold Moritz Expert

Agreed, luckily Jacob had multiple xls and could give me one to send out to Peter and Tom of Micromounters New England, who do the EDS gratis for local minerals sent to them by members. Slowly the collective we are backing up or refuting old claims unsupported by data (or lost data), which are now preserved here. Makes me want to send them a bunch of what appear to be common zircons, which are in pegs everywhere in New England.

22nd Oct 2019 17:57 UTCThomas Buchholz

In working on minerals of the Wausau Complex in central Wisconsin, I used to frequently run across xenotime, generally associated with zircon.  Despite the small sizes of the crystals found, xenotime has one characteristic that (if developed) will help to distinguish it from other species:  its perfect cleavage on [100].  Sometimes only a hint of a cleavage may be visible as a thin line parallel to [100], but if observed this has proven to be a reliable indicator. 

22nd Oct 2019 19:39 UTCChester S. Lemanski, Jr. Manager

Anybody entering/entered the new species to the locality page? How about the analytical readouts to that same locality? Thanks!

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