How can we differentiate between calcite, dolomite, siderite, magnesite and ankerite minerals in carbonatite rocks in thin section under optical microscope?
For an overview of carbonate mineral staining techniques in thin sections see attached screenshot
Thank you, we can distinguish carbonate minerals from petrography by giving Alizarine red staining on the thin section. The color that appears will reflect the type of mineral. For dolomite, the color of the staining will not change.
Alizarine red staining can be used for aragonite (no reaction), siderite (dark brown to black, normally without staining to determined on its semiopaque optical behavior due to Fe oxide-hydrate in the sediments. The solution consists of alzarine red + 30% NaOH (boil it). Before use it on the thin section you need to treat it with diluted HCl.
Mg calcite shows up in purple.
Combined used of AS =alizarine S + K-ferricynide = KFC
Calcite (no Fe, no Mg) AS = pink to pinkish brown KFC = no reaction
Cacite (Fe-bearing) AS= pink to pinkish brown KFC = light blue to deep blue depending on the Fe content
Dolomite AS = colorless, KFC = colorless
Dolomite (Fe-bearing, ankerite) AS =colorless, KFC=bright blue,mauve
HGD
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