Apart from explanation above, i just want to add a known technique if u work with synchrotron, it called anomalous dispersion. Example: Co and Fe, which is 1 electron difference, fFe(Q)/26 ~ fCo(Q)/27, is indistinguishable. But by choose the wavelength just below the Co absorption edge, it can create 6 electrons difference in scattering factor (Co-6e-).

Generally speaking any atoms with comparable electron number (=Atomic number) are difficult (not impossible though) to distinguish due to the similarity in the scattering factor curve. Also consider the oxidation states. I would say any element from approx. 24-Cr to 28-Ni will be difficult to distinguish from 26-Fe depending on the oxidation state.

XRF or a SEM-EDX may help...  

Regards 

Dominique

Dear Dr. Sabirov,

I agree with Dr. Ectors, however a big difference will be observed in magnetic susceptibilty measurements (SQUID measurements) if this technique is available to you.

Best regards,

Pedro Grima

Apart from explanation above, i just want to add a known technique if u work with synchrotron, it called anomalous dispersion. Example: Co and Fe, which is 1 electron difference, fFe(Q)/26 ~ fCo(Q)/27, is indistinguishable. But by choose the wavelength just below the Co absorption edge, it can create 6 electrons difference in scattering factor (Co-6e-).

X-ray crystallography is sensitive to the electron density within the unit cells of the crystal. Atoms with a small difference in the total number of electrons are hard to distinguish. This effect holds especially for all elements directly neighboured in the periodical system. For Mn and Co there is almost no chance to be distinguished from Fe, and even Cr and Ni is hard. If there are three or more electrons as the difference and you assign the site with a false kind of atom, you will be able to see effects in the refinement or in the thermal displacement parameters.

Apparently, you examine crystals of natural minerals. These often contain atom sites occupied with atoms of several different elements. It is essential to examine the crystals in a scanning electron microscope via EDX spectroscopy. If larger specimen or samples are available a classical chemical analysis is the best way to get information of the different metals present. X-ray work alone will not give a reliable result.

Thank you to all colleagues for helpful advice

Dear Dr. Sabirov,

Below is the link to helpful article. In this work authors analyzed different metals: light (Ca, K, Na, Mg) and some  heavy (Mn, Co, Fe, Ni, Zn. Cu) in protein structures.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2872550/

In your case a very important parameter would be the diffraction resolution. At high resolutions better than 1.0 Angstrom, one should see difference between carbon and nitrogen, between nitrogen and oxygen (difference is only one electron). The nature made all metals different, and even one electron gives differences in ligand coordination (number of interactions) as well as differences in the distances. Check the Table #3. So, for example Cu and Zn have very similar oxygen or nitrogen distances, but they have different coordination geometry. My point is that there are differences between metals, and at a very high resolution crystal structures one should be able to measure those differences.

I agree with others, the most easy and the best way would be Fluorescence scan, or collecting Anomalous data below and above the absorption edge of particular metal.

But my feeling is that, it is not what you are asking for. You are looking for the metals which would not change the diffraction pattern. And that brings to a question: How pure are your minerals (samples)? If different metals are involved in the formation of the mineral, than you have average of two or maybe several metals. And that could be a source of the problem, that you do not see differences in diffraction data.

Good luck!.

Dear G. Minasov,

Thanks You for Yours consulting. Really, I study the crystal struture of the solid solutions obtained from acidic solutions of the polymetallic samples. X-ray diffraction pattern contains X-ray reflections forbidden by the symmetry of the space group. I reduce space group symmetry and attempt to determine crystal structure in the frame of the software SHELXE. In some case the reasonable results were been obtained. But in the other when the many forbidden   reflections were observed I don't receive useful results: non-metal atoms are determined, but metal atoms have unphysical values.

I try to define relationship between the replacement disorder (numbers and type of the mutually replaced metal atoms) and number of the forbidden X-ray reflection. I hope to  receive posite results.

Best regards,

V.S.    

Dear Dr. Vakhobjon Sabirov,

Would you mind to attach one of the ur data together with the element information?

Dear Maykel Manawan,

Thank You for your offer. It's possible. I have to prepare the necessary data and then send them to You.

Best regards.

Dear Dr. Maykel Manavan!

Within that site,I can not send to you the X-ray data file. Can you give me an usual e-mail adress.

Thanks, 

Dear Dr Vakhobjon Sabirov.

This is my e-mail adress: [email protected]

Dear Maykel Manavan!

I sent to You X-ray data and results of chemical analyses of the productive solution. Crystals belong to the solid solution of the melanterite, i.e. (Fe,X)SO4 7H2O. Crystal structures of the 2 solid solutions were determined. In that case, I exam all d-metals, but not succesfully.

Best regards,

V.S.