What is the difference between calcite and dolomite

Calcite is invariably twinned but the twins do not show at all orientations. The largest grain is oriented so many of the twin lamellae are at extinction black in XP. Very high order interference colors -- high order pastels -- show along the not extinct twin lamellae. The large grain to the upper left is oriented such that twins do not show. This grain has interference colors that are of such high order that they appear white. Epidote, Dolomite and minor Pholgopite in a Marble. Another cause for the difference is the cation substituting for Mg in the dolomite mineral.

Keywords: Calcite; Carbonate; Dolomite; Raman spectroscopy. Abstract Raman spectroscopy was used to characterize and differentiate the two minerals calcite and dolomite and the bands related to the mineral structure.

This is possible because the atoms of different elements may be the same size, or nearly so. Calcium and magnesium are two such elements. When calcium carbonate crystallizes, calcite crystals are the more likely result. But if enough of the element is present, magnesium atoms can substitute for some of the calcium atoms, and the result is calcium, magnesium carbonate, or dolomite.

This isomorphic substitution comes into play in limestone and dolostone. Limestone is the most common calcium carbonate rock. It forms on the floors of oceans, which are often made partly of the remains of shelled sea creatures. It is almost always somewhat impure, yet limestone is one of the major sedimentary rocks throughout the American Midwest.

We quarry it, use it for road material, manufacture cement from it, cut it into building blocks, and use it for ordinary public buildings. Midwestern limestone is a tan or buff color, and is also commonly used in home construction. When limestone has few impurities, it is snow-white, or nearly so, and we use it for grave markers, monuments, and major public buildings, like the presidential memorials in Washington, D.

When subjected to heat and pressure, limestone recrystallizes enough to form a harder rock with a sugary texture that we call marble. Artists love it as a carving material, especially when it is snow-white. So we tend to call sedimentary calcium carbonate rock with colors ranging from gray to tan to white limestone. But is it?

The problem is that calcium carbonate can be impure to the degree that it constitutes a different rock, dolomitic limestone or, as scientists now call it, dolostone. We have even named a whole mountain range in southern Europe the Dolomites! They are of particular interest to mineralogists because this is where the mineral dolomite was first identified by D. He recognized it as something unusual, as it was a carbonate that contained both calcium and magnesium. Both the rock and the mountains in which Dolomieu had obtained his samples were named after him.

During the development of calcium carbonate limestone, other elements are present and some of them get into the calcium carbonate structure.

One of these is the metal element magnesium. It so happens that magnesium atoms are similar enough in size to calcium, only slightly smaller, and its electron valence matches that of calcium. This means magnesium can substitute for, or take the place of, some of the calcium in the molecular structure of the limestone.

It actually bonds within the molecular structure, becoming a permanent part of the structure. This differs from elements that are simply impurities trapped in the limestone rock. When enough magnesium substitutes for calcium in the limestone, the rock is no longer limestone.

We now call it dolostone. It also forms in lovely crystals, but not in as wide a variety as calcite. We also use dolomite in its massive form, dolostone. The first question is relatively easy to answer. Calcite responds vigorously to acid, while dolomite responds less vigorously.

Calcite is 3 on the Mohs Scale of Hardness, but dolomite is Mohs One other difference you may see is the smoothness of the crystal faces on your specimen. Dolomite crystals, because of an unusual internal structure, may have slightly curved crystal faces, while calcite does not. These are some simple tests you can use to determine the identity of a carbonate you own. The second question is considerably more difficult to answer. Limestone and dolostone are both carbonate rocks, but externally there is little difference.

The distinction really lies within the atomic structure of these carbonates. This is possible because the atoms of different elements may be the same size, or nearly so.

Calcium and magnesium are two such elements.