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MineralsLapis lazuli

29th Sep 2014 01:17 UTCJosé Zendrera 🌟 Manager

I think Lapis page http://www.mindat.org/min-2330.html needs some retouching. Have no much sense speak about cleavage talking about a rock nor give Miller indices refered to undetermined crystal (supposedly lazurite), isn't it?

Maybe to avoid misunderstanding would be clearer if Lapislazuli page text starts by defining it as "A rock composed by ..." as is clearly said in chert page http://www.mindat.org/min-994.html , in marble page http://www.mindat.org/min-9507.html , and other rock pages.

29th Sep 2014 03:46 UTCDoug Daniels

The problem is likely due to the references to hauyne as the major (maybe?) component, and thus the properties MAY be apparent in the rock made up of it...but I'm just grasping at straws with that.

29th Sep 2014 11:16 UTCAlfredo Petrov Manager

Although many people currently use lapis lazuli as a rock name, the original reference was just to the mineral species comprising the blue component.

29th Sep 2014 13:59 UTCVandall Thomas King Manager

The reference to Fischer calling lapis lazuli a rock has been deleted from the lapis lazuli page. As Fischer was the first person who declared lapis lazuli a rock contrary to previous systematic mineralogy books treating the blue mineral as the species, one could dismiss the article as an "errant" mistake assuming that lapis lazuli had to include the minerals it was associated with. If that were the case, we wouldn't have any minerals as minerals are always associated with something else, even if it is merely sand. The Yale U faculty of the nineteenth was particularly fond of introducing new mineral names and while they were essentially the IMA of their time, many of the minerals that they named were based on the research reports of others. Dutifully, they did try to honor the authors of the articles although they sometimes got the spellings wrong schwartzembergite instead of schwartenbergite or naming minerals for inconsequential authors such as "C. Tenger" whose modern identity cannot be traced. The color inspired name "lazurite" was unnecessary when introduced by Dana. The Dana's did like one word names, however, despite the senior Dana trying to create a binomial nomenclature for minerals. Somehow at Mindat, lazurite has been re-christened a variety of hauyne instead of making all lazurite "erroneously reported" in light of recent studies that there are virtually no S-dominant members of the group that have been verified. The upshot is that lapis lazuli isn't a rock, it is a traditional mineral influenced by a single article trying to suggest that all of the previous studies of lapis were made on the calcite, pyrite, etc. portions of the specimen. The analyses from the nineteenth century certainly look like analyses of pure material.

29th Sep 2014 15:33 UTCJosé Zendrera 🌟 Manager

The text of lapislazuli page is now better but still a little confusing. Even if in ancient times the name was created to lazurite, from Haüy's times lazurite has his own name and lapislazuli is mostly used to name a rock rich in lazurite but also containing another blue mineral (afghanite) besides other minerals (calcite, pyrite, etc)

Anyway, if lapislazuli is considered as synonym of lazurite, some corrections could be done:

- In lapislazuli page http://www.mindat.org/min-2330.html says lustre is "Sub-Vitreous, Greasy" and in lazurite page http://www.mindat.org/min-2357.html lustre is defined as "Dull".

- In lazurite page http://www.mindat.org/min-2357.html can read: "Lazurite is the blue component of the 'gemstone' (or, more accurately, decorative rock) Lapis Lazuli, which is a Lazurite-Calcite-Pyrite rock."

So what, Lapislazuli is a rock or a mineral?

29th Sep 2014 22:33 UTCOwen Melfyn Lewis

My understanding and such evidence as I have is:

1. Lazurite is a mineral of the cubic system that forms crystals (in my experience, mainly dodecahedral but other cubic forms occur). Those crystals I have examined are midnight blue. Some cut and polished pieces, under strong light and magnification, show one or two very fine veins of a a lighter blue (exolved?)

2. Lapis lazuli is an aggregate of several minerals of the sodalite group. It's predominantly lazurite, but in variable granular mix with hauyne, nosean and sodalite. It is striking for its ulltramarine blue colour. It is frequently found in association with pyrite, diopside and calcite, singly or in some combination that may or may not be intermixed with the lapis lazuli. Being a rock, lapis lazuli is massive and shows no cubic symmetry.

3. Hauyne, in those crystals I have examined, shows the cubic form which have a well-saturated blue but lighter and without the unique richness of ultramarine.

4. Nosean, I have not examined and know only from the standard reference works.

The lazurite and the hauyne I have seen show different characteristics.It is therefore worrying to hear that mineralological opinion is coming around to the view that they are one and the same thing. I am sure that a chemical analysis has been done that supports this view but I wonder what the statistical strength of that analysis may be? How many specimens of each and from how many different localities around the world have been identically tested and the results collated to come to this new opinion? Has the paper been publicised and is it possible to get hold of a copy?

The difference is colour and and crystal form almost certainly have their masis in subtle differences in chemistry and,at the atomic level, difference in the processes of all light absorbtion or colour formation - or both in some combination of processes. Dr Nassau commented briefly on the processes at play in producing the ultramarine colour (now not only understood but synthesised). In short, it results from the formation of polysulphide units of three sulphur atoms. It is deepened by raising the sulphur content (and reduced by lowering it). It's not obvious to me how this squares with hauyne and lazurite being the same thing. It does square with with the colour of lapis lazuli resulting from a mix of (mainly) lazurite, hauyne, nosean and sodalite.

Can we keep digging please, Van? Sometime one has to to come out into the daylight.

29th Sep 2014 23:13 UTCRob Woodside 🌟 Manager

Van, Was Lazurite introduced by Dana or by W. C. Brögger und H. Bäckström (http://rruff.info/uploads/Zeitschrift_fur_Kristallographie_18_1890_231.pdf)?

When did Fischer turn Lapis Lazuli into a rock?

Owen, the "Lazurite Problem" has been around at least since 1970, when Strunz published the Lazurite formula with dominant sulfate. If sulfate is dominant in the sodalite cages, it is Hauyne. It wasn't until 1985 that Lazurite was defined as an unobserved sulfide dominant calcian sodalite (Hassan I, Peterson R C, Grundy H D (1985) The structure of lazurite, ideally Na6Ca2(Al6Si6O24)S2, a member of the sodalite group, Acta Crystallographica, C41, 827-832). Here both SCXRD and EMPA were used to find the cage contents of Baffin Island and Afghan material. Again sulfate was dominant. The S₃ is, like most colourants, a minor constituent.

The 'mineral' Lapis Lazuli or Lazurite is an opaque, non fluorescent, ultramarine to midnight blue variety of Hauyne with a bright blue streak.

30th Sep 2014 13:20 UTCVandall Thomas King Manager

Yes, W. C. Brögger und H. Bäckström created lazurite from lapis lazuli and Dana's (1892) use of the name assured its ascendency. Looking at the actual literature, I don't find that H. Fischer (1869) , Neues Jahrbuch fuer Mineralogie, page 344-347, was all that critical of lapis lazuli and he does speak of lapis-lazuli crystals. My scientific German isn't up to reading his criticism as to whether it was his intention to formally discredit lapis-lazuli. He was merely reporting on his microscopical studies and the kind of rock that lapis-lazuli occurred in. See original at link: http://books.google.com/books?id=ZhgFAAAAQAAJ&pg=PA568&dq=neues+jahrbuch+1869&hl=en&sa=X&ei=C5kqVOb-H6np8AG0sICACQ&ved=0CCQQ6AEwAQ#v=onepage&q=lapis&f=false

The rock motif was followed by Ferdinand Zirkel (1873) Die mikroskopische Beschaffenheit der Mineralien und Gesteine, page 165 and I don't see very much to suggest he wanted to discredit lapis lazuli as a species, so much as there was quite an interest in the petrology of the occurrence. Zirkel's brother-in-law, Hermann Vogelsang (1873) wrote a comprehensive study of lapis lazuli in "Ueber die naturlichen Ultramarin-Verbindungen", Med. Akad., Amsterdam, v. 7, page 161, but also issued as a separate publication: http://books.google.com/books?id=EWdHAAAAYAAJ&printsec=frontcover&dq=Ueber+die+nat%C3%BCrlichen+Ultramarin-Verbindungen&hl=en&sa=X&ei=3J4qVLDICvSZsQTOuYDwBA&ved=0CB0Q6AEwAA#v=onepage&q=Ueber%20die%20nat%C3%BCrlichen%20Ultramarin-Verbindungen&f=false

gluck auf!

30th Sep 2014 14:46 UTCOwen Melfyn Lewis

Thanks for that, Rob. It was clear and helpful. Sadly and not for the first time, it seems as though the imperatives that drive the reform and development of mineralogical nomenclature are at variance with the imperatives of some other group (e.g. gemmologists, industrial chemists etc). who may have a vital interest in the same stuff but are driven differently and thus can benefit from differences in nomenclature from the strictly mineralogical. Sometimes, there is a push for greater differentiation in nomenclature (coming usually from a need to differentiate variances in colour through the understanding of their causes (e.g.lazurite/hauynite/other sodalite group members, forsterite/peridot etc.). And, sometimes, there is a need to relax the strictures of the mineralogical nomenclature (it would be distinctly unhelpful for gemmology to introduce the thirty-five - as at my last count - species of tourmaline to the gemmological nomenclature.

It occurs to me also, not for the first time, that the study of minerals from the unit cell down to the sub-atomic variances that cause many colours and colour changes may well be best carried out with material of synthetic rather then natural origin. since absolute uniformity of composition from sample to sample is important during the research. Whether that approach might benefit those studying mineralogy is for others to say but it seems worth a thought. Nature runs a dirty kitchen with many haphazard occurrences.

But to return to the specifics of lapis lazuli, ultramarine, lazurite and related minerals. A synopis of the findings of the chemistry, physics and crystallographic luminary, Kurt Nassau are as follows.

- Lapis lazuli is the gem form of the mineral lazurite. It is an aggregate of variable composition, mainly lazurite but also containing grains in some minor combination of hauynite, nosean and sodalite. Also commonly present in lapis lazuli are inclusions of calcite, diopside and pyrite.

- In a work published in 1984, he gave the general formula for lapis lazuli as (Na,Ca)₈(Al,Si)₁₂O₂₄(X), where X =SO₄ for hauynite and nosean, (S,SO₄) for lazurite and Cl₂ for sodalite. This is essentially the same as that determined by Hassan et al in 1984 (pub 1985) except for a doubling of the (Al,Si) content. For what the structural significance of that doubling might be, I seek advice.

- In his seminal work, 'The Physics and Chemistry of Color', pub 1991, Nassau gave the formula for lazurite as (Na,Ca)₈(Al,Si)₁₂O₂₄((S,SO₄,Cl)_x), equating the chemistry of lazurite with that of r4444444lapis lazuli.

- Ultramarine (as well as being a colour description) is a name applied to the synthetic form of lazurite used as a pigment, engineered to show the purest form of that colour, Outlining the precursor chemicals for the synthesisation, Nassau gives the formula for ultramarine as CaNa₇Al₆Si₆O₂₄S₃SO₄. Ca is proportionately increased, as is S.

- The minor constituent S is the essential chromophore, developing the ultramarine colour as an anion-anion charge transfer in the following way. The sulphur bonds as the polysulphide S₃. Sulphur, in its charge-balanced form, has the orbital configuration of 3s²3p⁴ so the anion S₃^- has a total of 19 outer orbital electrons. A transition among these orbitals results in a strong absorption of incident energy (light) around 2.1eV (wavelength 600nm +/-). This selective absorption causes the reflection of incident light by the material to contain only those energy levels/wavelengths that the brain interprets as the ultramarine colour.

- If the material is engineered to reduce the sulphur present in the molecule from S₃ to S₂ (or less) - i.e. hauynite - the colour intensity is reduced and may also acquire a greenish hue. Conversely, if the Ca and S levels present are raised, the colour is deepened (towards the midnight blue commonly seen in natural lazurite?).

Such work is not trivial and its importance in other fields than mineralogy is considerable. Accordingly, though it is hardly for me to say, it does seem that scientists in these other fields may not wish to follow the mineralogical determination that the name lazurite shall be abandoned in favour of subuming its meaning into that of hauynite. If this path were to be followed a useful (essential to some) distinction would be lost, I think.

One other point is worth a mention perhaps. You state the mineralogical view that lapis lazuli shows no fluorescence. That is not the experience of many gemmologists, who do find UV fluorescence (in a variety of colours) to be present weakly in *some* specimens. This would be consonant with traces of some other members of the sodalite group being present in small amounts in lapis lazuli as these are known to be sometimes UV fluorescent. Arem has also reported a yellowing glow in the streak under X-ray illumination.

I'm strongly aware that I put all this on a 'mineral' talk page of a mineralogical forum. I do so because I find the cross-fertilisation of knowledge and and approaches between specialisms is often helpful. It's the main reason (apart from the good company) that I hang out on Mindat. This sort of discussion puts me in mind of the three blind men coming across an elephant for the first time. One grasped a leg and said. "Elephant is of the tree species'. The one who had grasped its trunk shouted, 'No! How could it be? It is obviously a snake species!'. And the one who stood just behind the elephant found difficulty in speaking his opinion at all, though it was, indeed, strongly held. Nevertheless, we learn as we stumble about. Trying, as far as possible to adhere to a common lexicon that is useful to all should enable us to advance our knowledge faster.

1st Oct 2014 01:30 UTCRock Currier Expert

Why waist time trying to find a definition that suits everyone. We will use the mineralogical one for our species pages and when there are other definitions of that species name that others use, in kindness to our brothers we can also add their definitions.

Jewelers use

Geologists use

Petrologists use

etc.

1st Oct 2014 13:45 UTCVandall Thomas King Manager

I agree, Rock. While many authors have been aware of the 19th century authors, giants in petrology to be sure, who discussed the petrological nature of lapis lazuli, there are far more authors have used lapis lazuli forl the pure blue mineral. It is apparent from Rob's and other's research that the definition of lazurite is the problem.

1st Oct 2014 14:30 UTCOwen Melfyn Lewis

Rock,

That's a very generous and liberal suggestion but work-ish and tending to the Tower of Babel? There are a slack handful of names for some species, let alone their varieties.

Let's start from the position that mineralogists do not recognise - but freely and often use - varietal descriptions. The formulaic differences between hauynite and lazurite are indeed slight and, given the vagaries of *geological* creation may be as much a matter of who publishes what rather than of any universal and fundamental truth. If on the burden of empiric evidence IMA concludes that lazurite can no longer warrant its previous status as a mineral species distinct from hauynite, well so be it - but retain the name lazurite as describing a sulphur-rich variety of hauynite. I think this is exactly what Mindat is presently doing. This allow databases such as Mindat to remain completely useful and clear in meaning to those whose interests are not primarily mineralogical.

A similar argument can apply to the continuance of peridot, annotated under species forsterite as a slightly Fe-rich variety (approx Fa_10-12) and of essential green colour. All interests are again served? One can think of others to add to the list.

So far, so good. Puritan mineralogists can simply ignore varietal annotations if they think it in their interest to do so whilst others continue to benefit from varietal distinctions that are essential to their purposes. N.B. There is no place in this scheme for any 'trade-name' that cannot be justified on a basis of scientific differentiation. Thus, alexandrite will find a varietal listing; 'Zultanite(tm)' and 'Czarite(tm)'will not. - though colour-change diaspore might. Any suggestions as to what might become of herkimer diamond et al? ;-)

So far, so good. But it seems to me that the nature of lapis lazuli as an aggregate(rock) really should not be even under discussion. Patently, by examination it can be seen to be so. Under magnification one can see differently coloured grains and some crystal forms. Below is a not very good pic of a not very good specimen - but it makes the essential point I think. It does not appear to be a monocrystalline structure or uniform composition. Do zoom the shot and get down and dirty with this.

There might be a 'reductio ad absurdum' position that a 'perfect' Lapis Lazuli is perfect hauynite var lazurite. But I would enjoy reading an argument set out to justify that position.

2nd Oct 2014 01:25 UTCJosé Zendrera 🌟 Manager

Thanks for all wise opinions and references offered here.

Although lapis lazuli is not recognized as a mineral specie by the IMA nor as a rock by the IUGS Commission on Systematics in Petrology and there is not an official authority to define the meaning of lapis lazuli, ergo this is an debatable matter, let me add some comments:

- Reviewing historical data we see that lazurite was officially baptized in 1891. Before that date, obviously lapis lazuli was used to name both the rock and the pure mineral. But what happened after 1891? How many authors say lapis lazuli to refer to lazurite? I don't know but suppose very few. Once lazurite was defined and recognized I think the scientific community has used his own name to describe lazurite and today no one mineralogist say "lapis lazuli" instead of lazurite.

- 4000 years BC, in the Middle Age and right now, in Afghanistan, in Egipt, in Munchen and in Tucson, miners, traders and customers, when they say lapislazuli they refer to a blue stuff containing a variable percentage of lazurite as is comercialized in 99% cases in the market, not to pure lazurite.

Then, why today continue using lapis lazuli as synonym of lazurite?

Wrote:

-------------------------------------------------------

> Why waist time trying to find a definition that suits everyone. ...

Is not to find a definition that suits everyone. Is to avoid one that currently is not used by nobody!

Under UVA can see some fluorescences of different sodalite group minerals and afghanite at right.

Under UVC lazurite seems have a light blue fluorescence. Red at right is calcite.

2nd Oct 2014 17:10 UTCRob Woodside 🌟 Manager

José, I agree with you about Lapis Lazuli and Lazurite. Lazurite may be a little like Galenite; but unlike galenite, Lazurite survived. Those fluorescent photos are most interesting. I haven't seen this blue fluorescence in such obvious Lazurite. What wavelength is UVC? Is that what is also called midrange?

2nd Oct 2014 19:06 UTCOwen Melfyn Lewis

Yes, thanks Jose. some of those pics make the case perfectly, that the specimen is an aggregate with strong fluorescence in localised areas where the minor fluorescent minerals of the sodalite group are in the aggregate and with little/none.from the parts of the aggregate that are sulphur-rich Hauynite (aka var. lazurite).

You have some lovely Lapis Lazuli that would cut and polish into some good pieces for daytime wear. You interested in selling a piece to me? :-) Seriously.

3rd Oct 2014 01:21 UTCJosé Zendrera 🌟 Manager

Thanks again for your comments.

Rob Woodside Wrote:

-------------------------------------------------------

> ... What wavelength is UVC? Is that what is also called midrange?

I used a "Way Too Cool" lamp. I think UVA is about 380 nm and UVC about 250 nm, both with filter.

Owen Melfyn Lewis Wrote:

-------------------------------------------------------

> ... You interested in selling a piece to me? ...

No, sorry, these pieces are to me fond memories of youthful travels.

Not all my lazurites have this fluorescence:

3rd Oct 2014 11:44 UTCJosé Zendrera 🌟 Manager

I see that finally this debate has been helpful. Text of Lapis Lazuli page http://www.mindat.org/min-2330.html has been improved and the confusing cleavage data has been eliminated.

Thanks to all who have contributed to this discussion.

I take the opportunity to add a link to a one of the very few photo reports of Ladjuar Medam Lapis Lazuli mines in Afghanistan:

http://www.philippoupin.fr/asie-2/lapis-lazuli-lor-bleu-afghan/

3rd Oct 2014 18:36 UTCRob Woodside 🌟 Manager

Thanks Josele, So UVC is Short Wave UV.

Perhaps the definition of Lazurite should be changed to, "opaque, long wave non fluorescent, ultramarine to midnight blue hauyne with a bright blue streak." Something else is going on with these short wave fluorescent Lazurites. More stuff to reseach!!!

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