Here is your essay on Carbonate minerals


The carbonate minerals do not form a homogeneous group while some are hexagonal in crystallisation, others are orthorhombic crystals and still some others are massive in nature.

1. Hexagonal carbonates:

The more important members are:


(i) Calcite. CaC03. (ii) Dolomite. CaMg(C03)2.

(iii) Magnesite. MgC03. (iv) Siderite. FeC03.

(v) Rhodochrosite. MnC03. (vi) Smithsonite. ZnCOs.

(vii) Ankerite. (Ca, Mg, Fe)C03.


Physical properties:

(i) All are rhombohedral crystals.

(ii) Colour. Calcite is colourless, dolomite is often tinged with yellow, Magnesite is white or colourless, Siderite is yellowish brown, Rhodochrosite is pink, white-green colour is found in Smithsonite and in case of Ankerite.

(iii) Lusture. Vitreous to silky in fibrous varieties.


(iv)Cleavage. Perfect, rhombohedral (3 sets).

(v) Hardness. Calcite-3, in others it is 3.5 to 5.

(vi)Sp. gravity. Low.

Optical properties:


(i)Non-pleochroic colourless. (ii) Ref. index. Low.

(iii) Bi-refringence. High, in calcite it is 0.18.

(iv) Twinning. Polysynthetic.

(v) Twinkling is usually observed.


(vi) Extinction. Depends on the orientation of the section.


(i) Iceland spar. Transparent ealcite.

(ii) Satin spar. Fibrous calcite.

2. Orthorhombic carbonates:

The common members are

(i) Aragonite. CaCO3 (iii) Cerrusite. PbCO3.

(ii) Witherite. BaCO2. (iv) Strontianite. SrCO3.

Physical properties:

(i) Colour:

White, yellowish and grey.

(ii) Lusture:

Vitreous but cerrusite shows admantine lusture.

(iii) Hardness:

5 in case of aragonite, 3 to 4 in case of cerrusite,witherite, and strontianite.

(iv) Sp. Gravity:

High in cerrusite (6), in others 3 to 4.

(v) Cleavage:

Distinct in some cases and poor in others.

Optical properties:

Nothing important.


Carbonates are usually secondary minerals, commonly occur as gangue minerals in ores of hydrothermal origin. But in sedimentary rocks they are quite important.

Important characteristics:

All the carbonates react actively with acids.

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