FMF - Friends of Minerals Forum, discussion and message board

[bugrock]

Per mindat in recent years, the term “Quartz var. prase” has come to mean green quartz where the green is caused by inclusions no matter what the inclusions are. Many examples are illustrated in mindat where the green is attributed to Hedenbergite or Actinolite, but for most examples the mineral causing the inclusions is not mentioned.

In northern Michigan at the Ojibway copper mine dump (Keweenaw County) there was a past find of quartz xls with green inclusions that are referred to as ‘Chlorite.' Looking into that name quickly reveals it refers to a group of minerals, not easily distinguished.

A few questions for discussion:

1) How well is the ID of the various green inclusions of quartz documented?

2) Why are green mineral inclusions so frequent in quartz? Perhaps this is just artifact. I know there are many other inclusions in quartz of other colors and types. Perhaps "green" minerals that play the role just happen to be more difficult to identify on sight.

3) Can anyone explain the distribution of inclusions within the crystals?
Some green quartz is uniformly included (or so it appears in the images I’ve seen). Others are more zoned. This is the case for the Ojibway mine “Chlorite-included” specimen now on my desk. When carefully examined the fine green inclusions appear to crudely outline the distal ends of an earlier generation of quartz xls, now enclosed in larger crystals. I suppose the speed of quartz crystal formation and the availability of the mineral that forms the inclusions are both factors.

I am not a quartz collector but any mineral of the “Copper Country” of Michigan peaks my interest.

We have in the copper mine dumps a number of green minerals that are not copper containing molecules. Soft amorphous amygdaloid inclusions etc. are commonly referred to as "chlorite", often not of interest, not to be confused with chlorastrolite (Green Stone) for instance or to be removed as "green-mud" potentially enclosing choicer items such as copper xls etc.

Is it not odd that if you enclose a substance ordinarily thrown over the shoulder in a quartz crystal it gains special "status"?

[Peter Megaw]

I can't speak to your Michigan material, but green inclusions in quartz...hedenbergite, actinolite and "chlorite" are quite common in skarn deposits worldwide (Seriphos, Dalnegorsk, Santa Eulalia, Naica, Charcas, etc.). These deposits all go through a transition from prograde development (anhydrous calc-silicate growth formed during rising temperatures) followed by retrograde development (falling temperatures accompanied by influx of water with hydration of many/most of the anhydrous prograde phases). The result is that early anhydrous garnet-pyroxene phases break down to hydrous clays, chlorite and amphiboles with quartz and some other fun species. One of the adjuncts of this is that unmineralized limestone domains get dissolved during the retrograde event (calcite being more soluble at lower temperatures) so voids develop into which euhedral (sorry John) quartz crystals grow...and these continue to grow through a long stretch of the process so that amphiboles and chlorite get included as phantoms. I suspect that many of the "hedenbergites" in quartz are actually actinolite...but since the system can return to prograde conditions with fresh injections of magma, there is a reasonable expectation for both prograde and retrograde green species to be present as inclusions. I'd bet that most of the calls on hedenbergite versus actinolite are based on color rather than x-ray analysis

[John S. White]

In addtion to what Peter has described, in my experience the vast majority of included quartz crystals that are green in color due to actinolite or some other green amphibole occur in Alpine fissure type deposits, excellent examples being the European Alps and the mountains of Nepal and Pakistan where fine wispy actinolite is often found in cavities of regionally metamorphosed rocks. Of late, Pakistan is also producing similar looking astrophyllite in quartz but it is brown to orange in color. At times the green color of inclusions in quartz is due to epidote but the crystals of epidote tend to be more pronounced and individuals easier to distinguish. Tourmaline is also noted as a green inclusion in well-formed (but not euhedral) quartz crystals.

Many of the Alpine type of actinolite-included quartz crystals show a distinct lessening of the amount of included material from base to termination, such that the tips of the crystals are free of inclusions. One can see other examples where the inclusions coat former terminal faces of a growing crystal thus forming one or more phantoms within the crystal. This type I would not expect to find in Alpine environments.

[Jordi Fabre]

I would like to highlight the Clinochlore or other members of the Chlorite family that are frequently present in the Alpine Quartz as inclusions or covering the Quartz.

Although the Mindat's definition mentioned by bugrock 'green quartz where the green is caused by inclusions no matter what the inclusions are', I would prefer consider 'Prase' the Quartz not tinted by green due to Chlorite inclusions as the specimen in the photo below, but the ones with an uniform green color due to fibers of Hedenbergite or Actinolite, instead lamellar crystals of Chlorites.

[David Von Bargen]

There is a reason why definitions of varietal minerals are not usually made by mineralogists.

Clifford Frondel in 7th ed. Dana's System of Mineralogy defines prase as:
is more translucent than plasma and has a leek green color. The color usually is caused by dense aggregates of minute fibers of hornblende: also by chlorite.

[John S. White]

There is a very good discussion of prase in the website The Quartz Page including photos. Use this link:
https://www.quartzpage.de/prase.html

[Pete Modreski]

John, that "The Quartz Page" is really an awesome source of info and photos--thanks for mentioning it, I was not familiar with it, nor with its originator, Amir C. Akhavan.

I was actually surprised to read (in several of these posts) that crystalline quartz with green silicate inclusions is what is commonly known as "prase" now. I was still in the mindset that this word was used mainly for cryptocrystalline quartz--but as (The Quartz Page and others) point out, "plasma" is a term available to describe that, and "current usage" is to use prase for the crystalline quartz. Alas, I guess I have been partly living in the past.

It looks like when one gets into these definitions and distinctions about green quartz, most of us will find it really necessary to make a trip to the grocery store to get some first-hand refreshers about exactly what color "leeks" are!

Pete Modreski

[Peter Megaw]

Like Pete I guess I thought of prase as an archaic term akin to carnelian, sard or morion in terms of antiquity and utility...one long since retired to the dustbins of history. Mineralogically however the stuff is fascinating and I would like to share a few examples from Santa Eulalia (San Antonio Mine) and Naica. They include a range of greeness...I believe reflecting a contrast between hydrated and non-hydrated species (pyroxene vs amphibole) and density of inclusion. The darkest one is almost black it is so densely included. I also note that similar inclusions affect calcite on the some specimens and in the final case there is just amphibole included calcite on garnet (Naica...minature). Do we call that "crase" or the people who worry about such things "crasy"

[Peter Megaw]

whoops...screwed up the loading function and got the punchline first!

[John S. White]

Peter's photos reinforce a point made in "The Quartz Page" and that is that the inclusions often appear to affect the development of the crystals. The shapes of the crystals in Peter's photos are typical for much included quartz. What is not clear is whether the shapes of the quartz crystals are due to growth conditions which also favor incorporating inclusions, or if the inclusions are responsible for the odd-shaped crystals.

[bugrock]

Really appreciate the site suggested by John White. Appears to be a work in progress.

Consulted George Robinson regarding the "chlorite" included quartz from the Ojibway Mine,
Keweenaw Co, MI. He stated that the inclusions have not been X-rayed to support 100%
identification. They may be a chlorite mineral or clay or something else. Regarding Peter's comments on Mexican material, George stated the following (extracted from e-mail of Dec 1):

"Peter's observation on the alternating pro- and retrograde metamorphic events in the complex metasomatic skarn formations are probably more fitting to those specific manto-type deposits he describes from Mexico more than can be directly applied to the Keweenaw, as we don't have skarns or limestone replacement bodies here in the Keweenaw. In a broader sense, however, there is some parallelism: chlorites and clays probably did form during relatively low PT conditions prior to quartz emplacement in the basalt-hosted Cu deposits and may have been available for incorporation into growing quartz xls. The metamorphic grade never got high enough in the Keweenaw to reach the stability fields for actinolite or hedenbergite, even though the necessary elements to form them were probably present in the system. Pumpellyite and epidote are about the highest grade indicator minerals observed."


A closer look at the Keweenaw specimen I have on hand shows very fine but not uniformly distributed green particles as well as some few courser inclusions
similar to but not nearly as large or well developed as those in the beautiful specimen Jordi has posted. Also there are a few small ring-like green inclusions in the Keweenaw piece. I did a bit of searching on mindat in attempt to find similar rounded inclusions and the closest I can come to that are one specimen from Japan. See: https://www.mindat.org/photo-157681.html


Not suggesting an ID can be based on the shape of the inclusions but thought the existence of spherical quartz chlorite group inclusions an interesting addition to this discussion.

[bugrock]

A side note on quartz inclusions.

The site suggested by John White does not mention copper in quartz which is known from the Keweenaw, but it is difficult to find large quartz crystals with these metal inclusions. If you are willing to use magnification however there are some nice examples known for this copper mining district. The copper can occur as rounded or
elongated globules that are new copper penny bright and look as if the copper was deposited in molten droplets within the quartz.

[Amir Akhavan]

Hi there,

I guess I should step forward now instead of lurking in the background.
So this is my first posting and hello to everybody :-)

I've found myself checking this forum frequently, so I thought I could just as well subscribe to it.

> Appears to be a work in progress.
And I will never ever be done with it :-)
I can only afford to show the most common inclusions, which by itself will take forever. Inclusions are not priority, there are other gaping holes that I need to fill first.

Very nice Naica specimen. I just gave away the only one I had to Anastasios Tsinidis (FMF member if I recall that correctly), so he would have to check if I tell nonsense ;-)

I'm not 100% sure that they include a chlorite group mineral, but I'm 100% sure that they do *not* include amphiboles or (even more unlikely) pyroxenes.
The specimen Tasos has now in his collection had a zonar distribution of the very fine green mineral, most of it was concentrated in a thin layer under the surface in a way that suggests a superficial deposition on the growing quartz crystal (that means rather low temperatures). Amphiboles and even more pyroxenes typically predate the quartz crystals and run through them as fibrous inclusions in a more or less random way (often pointing away from the base of the crystal/matrix).

So I personally do not call them prase, but since prase is such a terrible wishy-washy term, I will not object to calling it so (and if I did one could still say "so what?" - there's no law against it). I just try to be somewhat consistent in my own taxonomy, as good as I can, and I'm not afraid to adapt and change it should I learn something new.

Does anyone know of a positive identification of hedenbergite in quartz? I've asked Gerhard Niedermayr about it, and will also ask Jaroslav Hyrsl (they both only found amphiboles in prase from Serifos).

BTW, The only identified inclusions of pyroxenes are aegirine (I've seen that myself) and spodumene.

I'll go to Japan on Tuesday, so if I don't respond immediately, don't worry.

Cheers
Amir

[bugrock]

Amir,

With increased participation we all learn more.

That is one of the main purposes of a forum in my view.

Would suppose identification of quartz inclusions is not high on the priority list for mineralogical institutions but it seems like an interesting subject.

[Jordi Fabre]

[arturo shaw]

Hi Amir, nice to see you around here as well (sad we didn't meet in München).

Say hello to your "roommate" from me. ;-)

In München I've been looking for "quartz with faces" (s and x faces...) and found some, but Carles Curto told me a story on a quite special quartz with pinacoid, perhaps he could tell us about it... even if it was not "prase". :-)

I am just expecting a prase quartz from Tasos at any moment (snail mail goes slowly). As soon as it arrives I'll post a picture in case it is of a different kind that those already in the thread.

Thanks for the info and for your page as well.

Greetings,

Arturo

[Tsinidis Tasos]

Hello to all!
Indeed, Amir's website is for me the best someone can find for information about quartz, and i am proud that a few of my specimens are pictured there.
I am looking for new and unknown mineral locations here in Greece and in a few cases green quartz shows up.The specimen in the photo comes from a small skarn zone near the village of Kato Vrondou in Kato Nevrokopi basin, Drama prefecture, East Macedonia, Greece. The specimen is completely included with a green mineral that I believe is chlorite.
Also chlorite is the coloring mineral of a few partly green alpine type quartz crystals from the area of Kato Nevrokopi.
I had long discussions with collectors here in Greece about prase quartz. Almost all of them use the term "prase" only for specimens that come from Serifos Island (hedenbergite inclusions). My opinion is that every quartz crystal that is colored green (from whatever inclusion) should be called prase.

[Tsinidis Tasos]

This is another specimen from the area of Kato Nevrokopi but from another location (Kresti hill). The color is a uniform light green and it is probably from chlorite inclusions.

[John S. White]

Tsinidis:

I really like the second quartz that you showed a photo of, very unusual habit.
Amir suggests that hedenbergite may be a misidentification, no one seems to know who first called the Seriphos inclusions hedenbergite and a pyroxene family mineral instead of an amphibole seems unlikely.

In my opinion the most fantastic quartzes from Seriphos are those that are partly green and partly amethyst.

[Tsinidis Tasos]

You are right Mr.White.
I am also aware of the analysis results of G. Niedermayr on the green quartz specimens from Serifos that are in the collection of Natural History Museum in Vienna. He found no hedenbergite as inclusions. Simply many people (including myself sometimes) say that the inclusions are hedenbergite, probably because it is the main matrix mineral for the green quartz.
I also don't know why there is no additional analysis from other scientists (especially from universities here in Greece). If hedenbergite is wrong then it should be corrected.
You are also right about bi-colored specimens from Serifos.They are really nice and not easy to find these days. I also like very much this smooth change of color from green to purple in the same crystal. I have also found similar color changes in quartz crystals from alpine type quartz veins in Kato Nevrokopi basin. In these crystals, color changes from smoky quartz to amethyst and (rarely) from smoky quartz to rock crystal (sorry for the bad photo).