Alizarin Red S Test for Dolomite and Calcite

The Alizarin Res S Test is a staining technique used in petrology to distinguish between calcite and dolomite.

How it works

• Alizarin Red S dye reacts with calcite (CaCO₃), turning it bright red.
• Dolomite (CaMg(CO₃)₂) resists staining or shows a weak reaction reaction (pink to color change)
• The test is performed under a microscope or on hand specimens.

Procedure

• Prepare a 0.1% Alizarin Res S solution in water or dilute HCL.
• Apply the solution to the rock or mineral sample.
• Observe the color change :
  • Calcite = Bright red
  • Dolomite = No change or faint pink

“If the rock contains both dolomite and calcite, only the calcite areas will stain red, while the dolomite remains unstained.”

Applications of Alizarin Res S Test

1. Differentiating limestone (calcite-dominant) and dolostone (dolomite-dominanat)
2. Identifying diagenetic changes in carbonate rocks
3. Used in petrographic thin-section analysis