FMF - Friends of Minerals Forum, discussion and message board

[bulwynkl]

Hi folks,

has anyone had any luck/experience removing gibbsite (presumably - whitish coatings - Al-hydroxides).

e.g. off Moroccan Vanadanites or Tasmanian Crocoite...

[Jordi Fabre]

As far as I know the Al-hydroxides are not easily removable at least without strong acids that probably will also damage other related minerals.

Please note that the white coats on Moroccan Vanadinites usually are carbonates not Gibbsite and that the Vanadinite is extremely sensitive to any chemical attack, so better dont try to dissolve them with chemical agents.

[bob kerr]

If it is gibbsite, then phosphoric acid will remove it - but like Jordi says it will no doubt impact the luster of the vanadinite. Many of the more recent crocoites from Tasmania have had gibbsite removed via the phosphoric route.

bob

[bulwynkl]

thanks folks,

I have a few things to try now...

confirm calcite v's gibbsite for Morocco, then pick an acid/concentration

I'll have a think about phosphoric and crocoite too.

literature suggests both crocoite and vanadinite more soluble in acid than base - might look at base to attack gibbsite.