Hafnon photo

Please delete the "hafnon" photo - its Hf-bearing zircon.

Was already deleted (but cache of mineral page was not cleared).
Actually, you could have changed to zircon.

Lukasz and Uwe,

What is the braking point in composition/structure to make zircon, hafnon? Please be gentle, I'm not a chemist.


TTFN

greater than 50% of the cation in the site, e.g. 49% Hf, 51%Zr is Zircon, vice versa would be Hafnon. This is valid for all solid solutions.

Chris,

I guess it was a no-brainer, but I thought I would ask it anyway.

I have read several times that zinc, and hafnium are the two most difficult elements to separate from one another. Is the reason/mechanism known?

Is it like separating Mills(Gold-digger, the _ _ _ _ _ with the Midas _ _ _ _) from McCartney's fortune. LOL.


TTFN

Zirconium and Hafnium have nearly identical chemical properties, and so are nearly impossible to separate by natural processes. Molybdenum and Rhenium are similar, and the rare earths also have very similar chemistry.

Chris- minor correction:

To be hafnon, the number of atoms of Hf must be bigger than the numbers of any of the other substituent big cations, which may be not just Zr but also Th, U etc. Because there are more than 2 possibilities, the cutoff cannot be guaranteed to be excatly at 50mol% HfSiO4. Just a majority of HfSiO4 in the solid solution relative to ZrSiO4, ThSiO4 etc.

Steve and Chris:
Zr and Hf are pretty well more chemically identical than any other pair of chemical twins, so yes, chemical processes are not efficient at separating them. Very tiny differences in energies may allow fractionation over a long enough period of time, though.

Physical processes are another matter, though: hafnium atoms are about twice as heavy as zirconium, and will diffuse more slowly in appropriate media, other things being equal...

Hi all!
In reality chemical processes sometimes and somewhere work very effective in separation of Hf from Zr.
I have information, that very disperse chemogenic zircon (var. arshinovite) of one deposits of Northern Kazakhstan has Zr/Hf ratio 200-250, while the ratio usual for zircons is between 1 and 2. So metallic zirconium from this locality concentrates is almost reactor purity (Hf is one of strongest absorber of neutrons within metals, and of course it is persona non grata in zirconium parts into nuclear reactors). Now the ores are represented by shists of low grade metamorphism, but originally they were soda lake sediments.

What about Hf ratios in a complex Zr-U-Th-Ca-TR silicate, the more components (end members) in solid solution, the lover at.% of Hf will produce hafnon. In other words, compound with composition (Hf_0.20Zr_0.16U_0.16Th_0.16Ca_0.06Y_0.16)_1.00[SiO₄] will be hafnon with 20 at.% of Hf.

According to this strontian and very polycomponent loparites [www.mindat.org] and [www.mindat.org] are formally tausonite while containing only ~9 wt.% SrO, but SrTiO₃ end member predominate in these crystals.

Unfortunately in real nature Hf-rich zircons aren't rich with other impurities and Zr+Hf : U+Th+REE+Ca+Nb+Pb+Bi is always not less than ~90 : 10...