FMF - Friends of Minerals Forum, discussion and message board

[Ed Huskinson]

Thank you Jordi - muchissimas gracias!!! ( https://www.mineral-forum.com/message-board/viewtopic.php?p=5238#5238 )

Back in 1977 I bought a little box of thumbnail azurites, pretty little things, labelled as from "Kerroucher", Morocco. I've carried that misspelling with me all these years, and it's nice to be able to set it straight.

Your specimen is quite beautiful. I notice that the azurite sits down in a little vug lined with crystals that look like dolomite. I have a malachite from Kerrouchen, part of the same lot, and it is lined with similar crystals. It appears to be a primary malachite, kind of uncommon. It's 4.3 cm by 3 cm wide. Here's a photo.

And this is one of the azurites, the only one on matrix. The specimen is 4 cm wide and 2.4 cm high. This one looks more like Carles' in that the breccia fragment has a bleached surface where the crystals are sitting.

The matrix is reactive, but only lightly, bubbling more in some areas than in others. Defintely not limestone, more likely a dolomite. That's why I figure the vug-lining crystals are probably dolomite.

I'll go next to the link you sent me.

Many thank-you's,

Ed

[Jordi Fabre]

Ed,

By my experience, your Malachite is not primary if this means for you: primary crystals of Malachite. Nor a pseudomorph of Azurite.
In mineralogical slang this kind of needles (acicular crystals of Malachite) are never named as "primary Malachite".

The matrix of the specimens from Kerrouchen is Dolomite and in my photo the small crystals in the vug also are Dolomite.

Jordi

[John S. White]

Why can't the malachite needles be primary? They certainly look primary to me..

[Ed Huskinson]

Thanks Jordi, for the access to the maps and for your responses to the Kerrouchen location overall. Your specimens from there are exemplary. As to the primary malachite issue, I've wondered about that. You see them together all the time, in specimens from Bisbee, and Tsumeb, all over, really. I never really gave it much thought until 1992, when malachite crystals from Kinsasha, Zaire were touted as being "primary".

PRIMARY MALACHITE

They were pretty, and I liked them, and bought one (thanks Ken). Close examination under direct bright Arizona sunshine seemed to disclose an almost blue interior to the crystals, but it is hard to tell, it's so dark green. Here're some photos of the piece.

Still, logic dictates that there is no reason why sometimes malachite would form, and sometimes azurite would form, and sometimes both minerals would form.

I have a specimen that came from Herb Obodda. It's label, the one I made for it, says:

Azurite over malachite after azurite on malachite

Because that's what it is. From Touissit (and I think it might even be from Puit Neuf, where Carles' originated), it is one of the "azurites" that shows the electric blue colour. The azurite occurs as a thin coating over malachite which has replaced azurite crystals. The whole shebang sits on 3 or 4 little malachite balls. Here're photos.

As I see it, without pontificating about the changing chemistry of the ore-forming solutions, whichever mineral (or combination thereof) shows up, well it just came up in the soup. And I'm glad for it.

Thanks everybody, and please feel free to chime in, post photos of pseudomorphs or primary crystals of your own. It's all about the minerals.

'sta luego,

Ed

[Les Presmyk]

The first time I remember seeing the term "primary malachite" describing malachite crystals occurred when specimens came from the Kombat mine, near Tsumeb, Namibia, at the same time the large malachite coated cuprites were found. This dates the term back to the 1980's. It has always bothered me, in maybe the same ways that John White is so fond of the term selenite.

Since all malachite is secondary (as an oxide of primary copper minerals), I have felt it is a minomer to refer to it as primary. They are either malachite crystals (acicular or otherwise) or pseudomorphs after azurite or whatever other mineral. Just my view, as a mining engineer with just enough geology and mineralogy to be slightly less than dangerous.

[John S. White]

Well the point, as I see it, is did these crystals grow as malachite from solution or are they pseudomorphic after azurite? The glassiness of them suggests to me that they are not pseudomorphs, then I suppose one has to assume that they are primary.

[Jesse Fisher]

In terms of ore petrogenesis, the copper-bearing minerals that are considered primary (or hypogene) are those formed by magmas or hydrothermal fluids rising from depth. The most common are chalcopyrite, bornite, enargite, and chalcocite. The secondary (or supergene) minerals are those that are the result of alteration of these primary minerals by the downward movement of meteoric waters. These secondary minerals can form in either an oxidizing environment above the water table or in a reducing environment below it. These minerals include native copper, cuprite, azurite, malachite, and many others. The processes responsible for the formation of these minerals also results in the concentration of the various metals originally deposited in the hypogene setting, making the supergene deposits some of the richest in terms of ore concentration and diverse mineralogy.

In this sense, malachite is by definition a secondary mineral, whether it is the result of the pseudomorphing of a pre-existing azurite or not. Calling any malachite "primary" is an oxymoron because it always forms in the supergene portion of an orebody.

[Ed Huskinson]

Thanks Jesse, for that cogent explanation of primary vs secondary mineralization. So we need to talk to whoever first used the term "primary" to describe malachite. He'd be the head oxymoron, eh?

I'll have a stern talking-to with him as soon as I find out just who it is. Or was. Thanks again Jesse. We have all benefitted from your reply.

Later,

Ed

[Jesse Fisher]

This is, at least, how I remember it from my courses in economic geology. That was, admittedly, a few years ago, now. If I misspeak, I trust that Peter will correct me.

[Ed Huskinson]

Jesse!!! you did not mis-speak (however you spell that). Your reply was great, perfectly to the point, constructive without being condescending, perfect. As I said, we all benefitted from your words. It's an interesting point though. When do "ore-forming solutions" stop? The wonderfully rich blankets of secondary enrichment over PCD's and in veins are attributed to circulating ground water, perhaps with some input by waning hydrothermal solutions. Are these the dying gasp of the last of the hydrothermal activity, or the onset of weathering and oxidation? I'l n'ya pas de quoi. It doesn't matter. The stuff circulates, oxidizes here, rearranges atoms/ions there, and voila! Ore!! It's all ore-forming. As Tony Potucek says, there are only 3 kinds of rocks (well, to a mining engineer) "Ore, Leach, and Waste". Har har!!

What must it have been like to work the outcrop at Tsumeb when it was first exploited!! Were there malachite crystals as big as baseball bats lining vugs you could walk around in?? Who knows, but it's fun to think about. You could whack cuprite crystals as big as softballs with the bats... Ah well, wishful thinking.

Keep it up, I enjoy your posts and read every single one of them. As a newbie, I'm catching up, am able to "play" only in my spare time (of which I have precisely none), but I get so bored writing here during the day that I jump at the chance to check a new post. So I read the back-postings as time permits, in an effort to keep duplication of a topic or observation to a minimum.

Thanks again,

Ed

[John S. White]

I think this is getting silly. Jesse is, of course, absolutely correct in terms of how primary is used in ore genesis, but as long as I can remember, when describing malachite, it has also been used to refer to actual crystals of malachite, rather than polycrystalline malachite replacements of azurite. In most cases the distinction is relatively easy. Primary malachite crystals are lustrous, have a perfect cleavage and can be quite translucent or even glassy looking. The difficulty arises when you have stalactitic malachite in radiating fibrous crystals. These begin to somewhat resemble malachite that has replaced azurite. But then there is another case which complicates this whole discussion, wherein one finds radiating fans of "primary" malachite growing as very thin coatings on large azurite crystals. These are often referred to as malachite partially replacing azurite. Well, they may be, but they may also not be.

[GneissWare]

I've never used the terminology "Primary Malachite" as its usage seems unnecessary. We don't talk about Primary Wulfenite although its also a secondary mineral with respect to ore genesis. When labeling Malachite, I simply call it Malachite and only modify the description when I am certain that it is pseudomorphing a earlier mineral species. This is the practice most follow with any other mineral. Why should Malachite be different?

[Jesse Fisher]

Unfortunately, I don't think this is silly at all. A precise definition of terminology is important to any science if we are going to communicate concepts in an unambiguous fashion. I understand the difference between malachite that has formed as a pseudomorph after azurite (or any other mineral) and that which has formed without a prior crystalline substrate. However, in the geological context in which these minerals form, the term "primary" has long been accepted to mean minerals of hypogenic origin. Malachite is not one of these. If a new term is needed to indicate the difference between pseudomorphic and non-pseudomorphic malachite, then let's come up with one. It shouldn't, however, be one already in use meaning something else. That just confuses the issue rather than clarifying it.

[Les Presmyk]

Thank you. That is my point. Even though there are cases of azurite after malachite after azurite, no one refers to an unaltered azurite crystal as being "primary" azurite.

[Jesse Fisher]

Les,
In this case I think it was primarily a marketing issue. If you give something a new name to indicate it is somehow different or more special than what one is use to, then it becomes more desirable. Just look at the "metaphysical" marketplace. How many names for plain old quartz can you find out there? Each one is invented to help sell a product.

[Les Presmyk]

Jesse, you are correct. When the material started coming out of the Kombat mine, the term primary was used to impress upon people these were malachite crystals, not pseudomorphs, in much the same way with the Zaire crystals that came out 15 years later. It is not that big a deal, really, because it is used within the hobby and will probably not be going away for quite some time. I have lived through labelling rules that originally felt that tourmaline and garnet were the species names and everything was a variety. Now, they are all individual species, which really makes more sense, except for those who still refer to all tourmalines as tourmaline, not the specific species.

[John S. White]

I would just remind Jesse that words have different meanings to different people. If a dealer or collector describes his or her malachite specimen as primary malachite, I know exactly what he or she intends. Most mineral collectors are not trained in ore petrogenesis and the terminology unique to that field is alien to most collectors.

[Ed Huskinson]

Yeah, good point John. I hadn't considered that. It goes to what Jesse and Les said about it (ie, the use of the word "primary") to be a marketing issue, unique to the description of the specimen at hand. Your description of primary malachite fits my specimen from Zaire perfectly: glassy, lustrous, perfect cleavage, etc. Hence the labelling. Now I get that.

So our discussion here diverted a bit from the purely mineralogical side of things and began to head down the economic geology/ore petrogenesis side of things. Sort of. But we mineral collecting explorationists do not have a forum for ourselves, so we're using this one. And it seems to be germane to the issue. If we wander outside the realm of minerals and mineral collecting a bit, well, I / we apologize.

So John, I think you've put the final nail into this thing, at least as far as primary malachite is concerned with regard to the collecting/dealing community. You've summed it up perfectly.

I'm still curious about this though: "When DOES the hydrothermal process end and the supergene process begin"? If there is an answer to this question at all. Maybe Peter will be able to shed some light here, or at least weigh in with an opinion.

For dealers and some collectors and mineralogists, bottom line, it comes to this: "Certain processes produced these minerals, and here they are for sale or trade". Then comes "Okay, so, what's the discount?" (Hey you have to ask, or they won't respect you...)

I've enjoyed this topic. I learned a lot, and it made me think. For this I thank everyone, especially Jordi, who started it all. I'm not saying it's over, just that the question has been answered to my satisfaction. Now I'm going to go look up struvite and enterolith...

Thanks again,

Ed