Learning Center What is a mineral?The most common minerals on earth Information for Educators Mindat Articles The Elements The Rock H. Currier Digital Library Geologic Time

Minerals by Properties Minerals by Chemistry Advanced Locality Search Random Mineral Random Locality Search by minID Localities Near Me Search Articles Search Glossary More Search Options

The Mindat Manual Add a New Photo Rate Photos Locality Edit Report Coordinate Completion Report Add Glossary Item

Mining Companies Statistics Users Mineral Museums Clubs & Organizations Mineral Shows & Events The Mindat Directory Device Settings The Mineral Quiz

Photo Search Photo Galleries Search by Color New Photos Today New Photos Yesterday Members' Photo Galleries Past Photo of the Day Gallery Photography

Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

PhotosWurtzite - Vienna Woods hydrothermal field, Manus Basin, Bismarck Sea, Pacific Ocean

21st Apr 2016 00:07 UTCMartin Rich Expert

Sphalerite, Chalcopyrite

Vienna Woods hydrothermal field 4, Manus Basin, Bismarck Sea, Papua New Guinea

Hmm, it seems, that I looked for such minerals in the wrong Vienna Wood! :-D

10th Jun 2016 03:32 UTCHarold Moritz 🌟 Expert

Beautiful crystals! The "wurtzite" looks like polysynthetically twinned sphalerite, note the multiple re-entrants around the "prisms". The crystals in this image http://www.mindat.org/photo-722324.html show the same morphology and have been confirmed by Raman and XRD as sphalerite. Examine your specimen to see if they part across the "prism"; this is the (111) face of sphalerite. Wurtzite makes hemimorphic crystals - a 6-sided pyramid with a pedion (like zincite) and shows cleavage along the pyramidal faces, which these crystals do not.

10th Jun 2016 21:36 UTCRob Woodside 🌟 Manager

Hmm... These certainly have the Thomaston Dam habit that has been long called "Wurtzite" We have it as erroneously reported with the comment:

"There has long been controversy regarding the identification of the brown, hexagonal micro-crystals of ZnS found here and generally referred to as wurtzite. This ID was first made by Myer (1962). Pete Dunn analyzed crystals in 1973 (see Yedlin 1973a and b) and concluded they are sphalerite pseudomorphs after wurtzite. Henderson (1979) showed diagrams of sphalerite crystals epitaxial on wurtzite, and the other way around, with a (0001) (pinacoidal) face of wurtzite matching a (111) (tetrahedral) face of sphalerite. In any case, the crystals from this locality, commonly labeled "wurtzite" were confirmed again in 2014 using Raman spectroscopy as sphalerite and appear to be polysynthetically twinned. The crystals are combined positive and negative tetrahedra of sphalerite twinned on a 6-sided (111) face. Note the re-entrant angles that circumscribe the "prisms" of these crystals, which are indicative of twinning. They also cleave along the tetrahedral form (parallel to the twin plane or across the "prism" stack of twins) whereas wurtzite's best cleavage is prismatic and is not evident here."

I speak from sad experience that the Fe contamination in ZnS messes up the Raman spectrum to the point that Wurtzite and sphalerite are indistinguishable by Raman. So I'm concerned about this "erroneous report". If it rests on Raman, it has no foundation. I don't think Wurtzite has ever been identified with x-ray diffraction from Thomaston. The Xrays have always shown Sphalerite? Please correct me if I'm wrong. This was formerly explained by saying that all the wurtzite had pseudomorphed to sphalerite either in situ or when the powder was ground to make the PXRD mount. Recently there's the suggestion that there never was any Wurtzite. It is all polysynthetically sphalerite mimicking hexagonal Wurtzite. They certainly look like twinned sphalerites to me.

If the IMA were to honour their commitment to disallow polytypes as species and not weasel out for "historical reasons", we would not have this difficulty as Wurtzite and sphalerite are polytypes of a single species.

10th Jun 2016 22:49 UTCHarold Moritz 🌟 Expert

Hi Rob:

I got the Raman done cuz it was easy and luckily free, but didnt know that the Raman result in this case would not be valid. I wrote the paragraph you quote and will amend it, thanks for that info. But as I cited, Pete Dunn did the XRD way back in 1972 for exactly the reason you mention. Here's the text:

The Mineralogical Record, Vol. 4, No. 2, March-April 1973

Yedlin on Micromounting

From Pete Dunn, at the Smithsonian: (dated December 13, 1972) 'It has been said that the wurtzite from Thomaston Dam, Connecticut, was of a type that changed to sphalerite under the crushing necessary for a powder x-ray photo. This thought intrigued me and I checked it out by taking a regular powder photo after crushing the sample in the usual fashion, and then took another x-ray using the Gandolfi camera which gives powder photos from single crystals. Result — both photos perfect sphalerite patterns, and identical, [emphasis added] indicating that the Thomaston wurtzite is really sphalerite paramorphic after wurtzite. I used two crystals with picture book wurtzite morphology which I collected at Thomaston myself.' (Ed. note: Change your labels.)

Now the only thin odd about it is Dunn's clinging to the "paramorph after wurtzite" conclusion, which I find bizarre given his XRD results and the known ability (even mentioned in my copy of Hurlbut and Klein) for sphalerite to polysynthetically twin on (111)! If this isnt what poly-twinned sphalerite looks like, then what does it look like? As I've mentioned, and is apparent in my photo and the one in question, these crystals are very translucent and show sphalerite parting on (111), in no way do any from Thomaston Dam (and I've seen hundreds) show wurtzite cleavage...how would that happen in a paramorph? Just cuz they are 6-sided crystals doesnt make them hexagonal symmetry. The Vienna Woods crystals were only visually IDed (see caption) and certainly do not show wurtzite's pyramidal, hemimorphic form; some have caps at the top, which seems only possible via twinning.

I dont really mind if IMA "keeps" wurtzite, but I would like to see crystals of it identified correctly so we can all know how to tell the "dimorphs" apart.

Thanks for your continued input on this matter. :-)

10th Jun 2016 23:33 UTCRob Woodside 🌟 Manager

Thanks Harold, That paragraph and reference you quote should be in the erroneous Wurtzite blurb.

It seems there's some work to do changing all the Thomaston photos:-(

Now this Black Smoker specimen has become POTD. At least the caption says "visually identified" and this comment thread is attached. POTD is supposed to be written in stone and unchangeable!!! I'll send a note to the owner asking it it might be x-rayed.

10th Jun 2016 23:48 UTCHarold Moritz 🌟 Expert

"Thanks Harold, That paragraph and reference you quote should be in the erroneous Wurtzite blurb."

Will do!

11th Jun 2016 05:36 UTCChristian Auer 🌟 Expert

Thanks for bringing this up.

I was aware about this problem and talked with Uwe Kolitsch about it. We decided to add the pic with this description (visually identified).

I`ll check the interesting master thesis on the Vienna Woods material from S.Steger (2015). I`m sure he made a X-ray.

If not, we luckily have a X-ray and luckily we have lot of material :-)

Will let you know the result ...

11th Jun 2016 06:21 UTCKeith Compton 🌟 Manager

Hi

While we at it here

Can we get the Manus basin listed under Papua New Guinea rather than Pacific Ocean.

Cheers

Keith

11th Jun 2016 10:08 UTCUwe Kolitsch Manager

> Can we get the Manus basin listed under Papua New Guinea rather than Pacific Ocean.

Thanks for pointing this out.

http://robertthornettgeography.blogspot.co.at/2014/03/deep-sea-mining_21.html

"... in the Manus Basin within the Bismarck Sea, part of PNGs territorial waters."

4th Jul 2016 07:25 UTCChristian Auer 🌟 Expert

Last week I got a response from Mr. Steger, who made his masters on the Vienna Woods.

He made many XRD analyses and identified BOTH, wurtzite and sphalerite in all samples. Those areas of the black smoker that were near the vent (with high temperature) spahlerite was dominant. Unfortunately he didn`t do any single crystal XRD as the species were often intergrown too.

He used also RAMAN but due to the high Fe-inpurity he didn`t get any good spectra.

Referring to his comment on the high temperature vent beeing more likely sphalerite I would suggest I stick to this species on the pic and make a side comment to this thread.

4th Jul 2016 14:07 UTCHarold Moritz 🌟 Expert

Interesting results, obviously Mr. Steger's goal was not to document the differences between wurtzite and sphalerite here, but at least sphalerite was found. Or perhaps, Rob, the presence of both, and "intergrown" argues they are polymorphs of the same mineral??

Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 25, 2024 14:00:06

Go to top of page