Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for EducatorsMindat ArticlesThe ElementsThe Rock H. Currier Digital LibraryGeologic Time
Minerals by PropertiesMinerals by ChemistryAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
Mining CompaniesStatisticsUsersMineral MuseumsClubs & OrganizationsMineral Shows & EventsThe Mindat DirectoryDevice SettingsThe Mineral Quiz
Photo SearchPhoto GalleriesSearch by ColorNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day GalleryPhotography
╳Discussions
💬 Home🔎 Search📅 LatestGroups
EducationOpen discussion area.Fakes & FraudsOpen discussion area.Field CollectingOpen discussion area.FossilsOpen discussion area.Gems and GemologyOpen discussion area.GeneralOpen discussion area.How to ContributeOpen discussion area.Identity HelpOpen discussion area.Improving Mindat.orgOpen discussion area.LocalitiesOpen discussion area.Lost and Stolen SpecimensOpen discussion area.MarketplaceOpen discussion area.MeteoritesOpen discussion area.Mindat ProductsOpen discussion area.Mineral ExchangesOpen discussion area.Mineral PhotographyOpen discussion area.Mineral ShowsOpen discussion area.Mineralogical ClassificationOpen discussion area.Mineralogy CourseOpen discussion area.MineralsOpen discussion area.Minerals and MuseumsOpen discussion area.PhotosOpen discussion area.Techniques for CollectorsOpen discussion area.The Rock H. Currier Digital LibraryOpen discussion area.UV MineralsOpen discussion area.Recent Images in Discussions
Improving Mindat.orgFerrisicklerite formula
10th Mar 2012 17:03 UTCVik Vanrusselt Expert
Shouldn't there be a comma between the Li and the Mn2+ ?
Formula written differently here: http://rruff.geo.arizona.edu/doclib/hom/ferrisicklerite.pdf
I'm a beginner in chemistry, how come there are different ways to write formulae?
Vik
10th Mar 2012 18:42 UTCAlfredo Petrov Manager
10th Mar 2012 20:09 UTCDavid Von Bargen Manager
http://rruff.geo.arizona.edu/AMS/amcsd.php
you will see two metal sites M1 and M2
M1 has an occupancy of 0.33 Li1+ atoms (rest are unoccupied/vacancies)
M2 has 0.66 of Fe3+ and 0.33 of Mn2+ (etc)
Structurally the formula should be written
Li0.33(Fe3+0.66Mn2+0.33)PO4
10th Mar 2012 23:37 UTCAlfredo Petrov Manager
11th Mar 2012 00:10 UTCPedro Alves Expert
something like: Li1-x (Fe3+x ,Mn2+1-x)Σ=1,00PO4
Where Li=Mn2+ and Fe>Mn
Pedro Alves
11th Mar 2012 00:13 UTCVandall Thomas King Manager
11th Mar 2012 12:45 UTCMarco E. Ciriotti Manager
Reference:
▪ Hatert, F., Ottolini, L., Wouters, J., Fontan, F. (2012): Crystal chemistry of olivine-type phosphates: a structural study of the lithiophilite–sicklerite series. Canadian Mineralogist, 50, (in press).
12th Mar 2012 09:04 UTCUwe Kolitsch Manager
12th Mar 2012 12:59 UTCAlfredo Petrov Manager
12th Mar 2012 14:01 UTCVandall Thomas King Manager
12th Mar 2012 15:54 UTCUwe Kolitsch Manager
12th Mar 2012 16:25 UTCPedro Alves Expert
and for the Ferrisicklerite case?
Cheers,
Pedro
12th Mar 2012 16:47 UTCPedro Alves Expert
just some questions:
is this formulae correct/applicable (for ferrisicklerite)?
Li1-x (Fe3+x ,Mn2+1-x)Σ=1,00PO4
as an attempt to balance the charges.
If yes, the Mn content is directly related with Li. And, the more Li is leached, the lower Mn we have. Resulting in ,when total Li leached, Heterosite.
In the most part of the cases, i believe, Mn is not leached (only Li). The 'loss' of Li affects the balance of the charges, which is solved by the Mn2+ oxidation to 3+. Is that correct?
Comments and corrections are welcome.
Thanks,
Pedro
12th Mar 2012 20:24 UTCVandall Thomas King Manager
4th Apr 2012 18:56 UTCJeff Weissman Expert
Van, by the way, I didn't know that purpurite and heterosite where "theoretical" :-D, re your message of March 10, 2012 07:13PM
4th Apr 2012 19:56 UTCRichard Gunter Expert
29th Jun 2012 06:06 UTCJeff Weissman Expert
Mindat is listing both sicklerite and ferrisicklerite as approved minerals with grandfather status. On the purpurite and heterosite pages it is implied that they are varieties, so what is the resolution to this contradiction?
1st Jul 2012 16:48 UTCPeter Haas
If you really prefer using variables in subscripts, please note that something like (Ax, B1-x) is wrong, because (1-x) B cannot replace x A - except x = b/(a+b) (where a and b are the charges of A and B, respectively), in which case the use of a variable does obviously not make any sense, or the charge is balanced by coupled substitution, in which case you'll have to obscure the formula further by introducing even more variables.
In other words: if you are using variable subscripts, you have to omit the comma: (AxB1-x) is correct. Note however, that this has exactly the same meaning as (A, B).
Now, if you still want to keep the variables, please also note:
(1) There is no need to keep the brackets in an expression such as (AxB1-x). In order to avoid confusion, the brackets should be omitted - unless you want to indicate that A and B are occupying a specific site, in which case they are better replaced by curly brackets though.
(2) You have to define x unambiguously, as this is not self-explaining. This condition (here, 0 <= x < 0.5) is an integral part of the formula.
Now, let's have a closer look at Rui's last proposal. Note that I have added the missing condition for x and also left out the comma, for the reasons explained above:
Li1-x(Fe3+xMn2+1-x) (PO4), 0 <= x < 0.5
This can be modified by applying simple mathematical logics (in fact, the following transformations don't have anything to do with chemistry):
First, the brackets can be omitted:
Li1-xFe3+xMn2+1-x (PO4), 0 <= x < 0.5
Note that I keep the bracket for the anion. This is to make clear that "PO4" is a single anion. Now, some of you might want to add that this is obvious anyway. Note however, that it is much less obvious when the mineral contains amphoteric elements, i.e. elements that can (and often do) occur both as cations and as constituents of oxoanions: in those cases, the bracket must be used in order to make clear what is meant. Instead of using the brackets when we (the specialists) think they are needed and leaving them out when we (the specialists) think they are not, we have decided to use them consistently.
Second, lithium and manganese have the same subscript and can be combined. Note that I need brackets now in order to indicate that the subscript applies for two cations (those within the brackets) and not only one (again, this is a mathematical convention, not a chemical one):
Fe3+x(LiMn2+)1-x (PO4), 0 <= x < 0.5
All those notations have exactly the same meaning. However, I still prefer to keep formulas as simple as possible and this implies avoiding variables in subscripts when they are actually not needed. If you could follow the discussion down to this point, you will easily notice that the formula written above has the same meaning as the one I add below:
(Fe3+,LiMn2+)(PO4)
We really should stop questioning our notations of chemical formulas every time we are asked a question about the meaning of a particular notation or about seeming discrepancies between our formulas and those found on different websites. Understanding chemical formulas of complicated minerals requires a chemical knowledge that exceeds what is taught on high schools. There is no way to simplify chemical formulas so as to be understood by anybody - pretty much in the same way as there is no way to guarantee that a phrase in a foreign language will be understood by anybody, no matter how simple it is written.
Consequently, there will always be questions from people who just don't understand the formula, no matter which notation we preferrably adopt, and ask us because they want to learn. Trying to adopt a simplfied notation in a fruitless attempt to avoid
such questions in the future will only raise more questions in the long run. More importantly however, it will also not resolve the respective person's problem; this still has to be taken care of by an appropriate explanation (which, in some cases, will be rather lengthy). There also will always be people who do not understand the formula and do not want to learn, but just spot a difference between our formula and the formula on another website and think that this alone qualifies as an error. Although I generally dislike smarties, this behaviour has to be encouraged as well, since there is always a finite chance that they did really find an error.
This said, we still need to answer one of Vik's questions:
It is the composition of a mineral (or, more generally, of a chemical compound) that is defined, but not the formula itself - a slight but important difference. Formulas are an important tool in a chemist's daily work and as such, they have to be flexible (in fact, if we have to be strict, we're mostly using systematic compound names, not formulas). The only requirement for a formula is that it must properly reflect the composition, but there are no definitions whatsoever concerning the level of detail or the notation. Even the IUPAC has surprisingly few recommendations on the formulas of inorganic compounds. They generally recommend to use sum formulas (i.e. formulas with a zero level of structural detail), because they are easily standardized (on the other hand, they also are horribly impractical for more complicated compounds). They also recommend (very amusing, actually) to write the individual elements in alphabetical order. There are many IUPAC rules for organic compounds (where they are sorely needed, not only to ged rid of the flood of superfluous trivial names), but they are entirely irrelevant for minerals.
16th Jul 2013 16:07 UTCJeff Weissman Expert
sicklerite and ferrisicklerite are listed on their respective pages as Grandfathered
yet, on the purpurite page is given "Intermediate alteration products were once thought to be valid minerals, but they were merely part of a continuous process of alteration: Ferrisicklerite and Sicklerite"
Is there an IMA decision on this, otherwise, need to correct the purpurite and heterosite pages
16th Jul 2013 18:24 UTCAlfredo Petrov Manager
One implication of this is that a "grandfathered" mineral ceases to be considered a "valid" species when any significant number of people express doubts about its validity, because then it's no longer "generally accepted" and so no longer fulfills the criteria for "grandfathering". Some mineralogical list compilers believe that all doubtful minerals should be kept on the valid species list until a formal discreditation is published. Zoologists, luckily, don't follow the same policy, or else there'd still be a section on unicorns in zoology texts. :-D
16th Jul 2013 20:48 UTCJeff Weissman Expert
In the case of sicklerite, the mineral does appear to be generally accepted as valid, in light of recent papers, for example see a discussion on the crystal-chemical structure of sicklerite that Marco mentions near the start of this thread , now published. Certainly the authors of this paper are knowledgeable in what makes a mineral valid, and did not suggest that sicklerite is not valid - hence by default sicklerite (and also by analogy ferrisicklerite) should be considered Grandfathered and generally accepted as valid, as these names continue to appear in and be used in the peer-reviewed literature as "valid" minerals. That said, perhaps a proposal should be made to invalidate these two as intermediates, until then, some consistency needs to be had in the MinDat database.
Hence my argument and suggestion that the entries in the purpurite and heterosite pages be modified, at least for internal consistency. I will do so accordingly.
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: March 29, 2024 11:32:20
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: March 29, 2024 11:32:20