Dear Mr. Elhadj:

Given the rhomb-shaped XX are calcite  floating in a matrix of micritic calcite, the textural and mineralogical hints are in favour of dedolomitization. Have you got also "limonite" which is typical of dedolomitization because of the missing opportunity of trivalent Fe to be accommodated in the carbonate lattice? Dolomite contains significantly ammounts of bivalent Fe which may  reach levels as much as  to denominate the mineral ankerite. Dedolomitization takes place under oxidizing conditions and disturbs the valence state of iron. It is another evidence for dedolomitization in this case.

I agree with your assumption

H.G.Dill

Dear Mr.  Elhadj,

It may be dedolomitization. That may be more believable if you can provide CL image at the same time.

Best wishes,

Yongbin

Thank you, dear colleagues for your answers!

Hi Youcef,

You can have more evidence if you use the polarized light in your microscope. If it shows a grey to blue (dark) color within the Rhombohedron, it means that you have a secondary porosity generated by the dissolution of your dolomite and this is what is referred to by the term "dedolomitization". 

Kind regards,

Salma

Hi Salma,

Thank you for the answer 

I may suggest that you may stain the thin section with Alizarin Red-s to distinguish to a large extent pure calcite portion, dolomite portion, and ferroan dolomite and ferroan calcite (if they are present) besides the suggestions given above other scientists.

Hi Narasinga

Thank you for the answer 

There is no single process that can be called "dedolomitization". The dolomite may be dissolved with calcite cement filling the pored or may be replaced by calcite (calcitized). It is better to describe these than to use an imprecise and basically undefined word. Your images ar unfortunately insufficiently detailed to determine the process tha has occuerred. The advice of other correspondents recarding CL and staining is worth following up.

Hi Braithwaite

Thank you for the answer 

yes, It might be dedolomitization.

Selma Ben Amor

dedolomitization is the transformation of former dolomite to limestones. or partial to complete transformation of dolomite to calcite on the scale of individual crystals. what you're referring to is just dissolution.