The iron minerals comprising iron stones contain oxides such as  limonite/goethite, hematite and magnetite and carbonates such as siderite, ankerite sometimes silicates such as chamosite 

.rhodochrosite  can be the manganese bearing mineral.

Are you able to access X-ray diffraction analysis? That would provide a very simple method to gain some idea of what minerals are present in your rock.

Dear Mr. Hossein,

More than 400 Fe minerals are known, but only Fe ore minerals with more than 15 % Fe (by definition of Kamphausen & Walther 1974) are relevant.

 I try and give you an overview of the minerals and their Fe contents in questions casting the potential gangue minerals such as quartz and non-Fe calcareous minerals aside:

•          Fe-oxide hydroxides

–        Goethite a  Fe3+O(OH) (62 % Fe)

–        Feroxyhyte Fe3+O(OH) (62 % Fe)

–        Lepidocrocite g Fe3+O(OH) (62 % Fe)

–        Akanganeite Fe3+7.6Ni0.4O6.4(OH)9.7Cl1.3 (56 % Fe)

–        Form „limonite“ when intergrown with Al (diaspore, boehmite), Mn (manganite, groutite, feitknechtite), Ga (tsumgallite)        

•          Fe carbonate

–        Siderite FeCO3 (48.2 % Fe) substitution of Mn, Mg, Ca

–        Ankerite Ca (Mg, Fe)(CO3)2 (26 % Fe)

•          Fe silicates

–        Chamosite Fe2+3Mg1.5AlFe3+0.5Si3AlO12(OH)6  (29 % Fe) „thuringite“

–        Greenalite Fe2+2.3Fe3+0.5Si2.2O5(OH)3.3 (44 % Fe) BIF

–        Minnesotaite Fe2+2.5Mg0.5Si4O10(OH)2 (30 %Fe) BIF

–        Stilpnomelane K0.7Fe2+3.3Mg1.4Fe3+3.3Si10Al2O24(OH)3·2(H2O) (29 % Fe)

–        Grunerite Fe2+7(Si8O22)(OH)2 (39 %Fe) BIF

•          Fe oxides

–        Magnetite Fe3O4 (72.4 % Fe), traces of V, Ti, Al, Mg

–        Maghemite g Fe2O3 (69.9 % Fe)

–        Martite g Fe2O3 (69.9 % Fe)

–        Hematite a  Fe2O3 (69.9 % Fe)

Frankly spoken, without a proper XRF, EMPA.....to try and find the mineralogical composition based on chemical analyses only means poking around in the fog and it is not really scientific.

With kind regards

H.G.Dill

Dear Ms Asoori Latha,

Thank you for your reply. We do agree with your comments. We assume that the constituent minerals of these rocks are mostly goethite and/or limonite, with hematite and magnetite. Although, goethite usually contains about 5–10 wt% SiO2, the studied geochemical data provide about 6.5–24.5 wt% (av. 15.7 wt%) SiO2, which is higher than the normal goethite (e.g., James, 1996) that means the studied ironstones have considerable amounts of glauconite or clastic quartz (SiO2). These ironstones have exceptionally higher MnO (3.8–11.68 wt%) with an average value of 7.66 wt%, these signify rocks contain considerable amount of manganese minerals, those may be rhodocrosite or braunite. Is this enough to specify these specific minerals only from geochemical data?

Dear Jana M. Horak,

Thanks for your comment. I’ll try to ponder over your way. Regards.

Dear Harald G. Dill,

Thank you for constructive and informative message. Really I am bit puzzle about my studied ironstone data. I’ve some limitations, especially EPMA, or other high precision analysis. In that case I’ve to depend only on geochemical (XRF) data. For that reason, I asked if you had any information about mineral analysis based on chemical composition. Regards.

I think that I can only reiterate what Dr Dill has said and I mentioned, that to define which mineral are present and I what proportions you need to have some crystallographic control, here a minimum of XRD data, but of course EMPA would provide this. I can't see that you can have confidence in resolving tis fi you don't have this data.

Sorry, it to be more positive! How large is this project?

jana

Dear Jana M. Horak,

Thanks for your realization. This work is the part of M.S. thesis of my student.

Regards,

Ismail

Dear Ismail,

Are you able to access X-ray fluorescence (XRF) analysis? That would provide a very simple method to gain some idea of what minerals are present in your rock

Dear Noor Haleem,

Thanks for your message. Yes, It's possible to access XRF analysis. If possible, please provide me your idea (methods) to gain the information of what minerals are present in rocks.   

Dear Ismail, I think the best way to identify mineral phases on sedimentary samples is the use of X-ray diffraction. As stated by Mr. Harald and Ms. Jana, you'll need some crystallographic control, at least some ore petrography. By chemistry only, at least some provenance context must be stated, to identify if it is more plausible to have limonite and/or goethite as minerals from weathered rocks, or hematite and magnetite as minerals for less weathered rocks. SiO2 content, by the, must be or be not associated with Fe2O3 in mineral structure, as much as CO2, SO2, etc. Low Ca, Na and low Al states against major contributions on feldspars and muscovite; low Mg against SiO2 content are stating against chamosite/chlorite or evem biotite as a main constituents. With no crystallographic control, there's no chance to guess right.

With 61.71–73.87 wt% on Fe2O3, the field sample or sample powder must be a very good indicator. Magnetite is always magnetic, as well as magnesioferrite, and trace color on porcelain plate is dark black. Hematite gives a reddish trace, while goethite gives orange brown trace. Limonite gives orange to yellow trace. The powder color enables to guess more or less on the right direction, but with no quantitative precision.

Petrography in reflected light, if crystals are larger than 20 micrometer, must give some answers too. But a good rietveld refinement on X-ray diffraction is even better.

Dear Cibele Montibeller,

Thanks for your remarkable observation of my question. I strongly believe it is more plausible to have limonite and/or goethite. I've precisely checked the trace color on porcelain plate, color almost align with goethite or limonite (nearly orange brown trace and light brown trace).  So, I am just waiting for XRD results to know the exact crystallographic control.

Regards.

Dear Ismail.

I think everybody has literally addressed your question quite clearly. X-ray diffraction may help you with the predominant Fe-minerals that might be present in your samples. By the way, only i you had highlighted the age of your sedimentary deposits, rock types and a bit of geological background of the area, little prediction can be drawn on the possible Mn and Fe-minerals present.

For instance, South Africa is predominantly characterised of the Palaeoproterozoic Mn-carbonates (Rhodocrosite and Kutnhorite with some silicate phases) and reduced iron.