Calcite


Mineral: Calcite

The word calcite is derived from a greek word Chalix. Calcite is a carbonate mineral having the chemical formula CaCO3. Crystal habit of calcite is crystalline, granular and rhombohedral. It occurs in a seemingly unlimited variety of shapes and colors. It constitutes a major portion of many of the earth's rocks.
Calcite is one of the forms of limestone. The crystals of calcite show a remarkable variety of habits in its shape including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. The structure of calcite group is stable at normal temperature and pressure with smaller metal ions. Calcite and Aragonite are polymorphous to each other. Although Calcite and Aragonite contain the same elements, they differ in crystal structure. Calcite forms trigonal crystals, whereas Aragonite forms orthorhombic crystals.
There are several varieties of it and the most common is scalenohedron, it appears like a double pyramid or dipyaramid but it is of different form. Calcite, like most carbonates, will dissolve with most forms of acid. Calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in cold water, acidity can cause dissolution of calcite and release of carbon dioxide gas. Calcite is intricately tied to carbon dioxide in another way. Since many sea organisms pull carbon dioxide from the sea water to accomplish this in a near reverse of the reaction above. This is fortuitous for us, as carbon dioxide has been found to be a green house gas and contributes to the so called green house gas effect. Environmentally then, By pulling carbon dioxide out of the sea water, this biological activity allows more of the carbon dioxide in the air to dissolve in the sea water and thus acts as a carbon dioxide filter for the planet. A significant amount of calcite precipitation in sea water is undoubtedly inorganic, but the exact amount that this contributes is not well known. Calcite and other carbonate minerals are very important minerals in the ocean ecosystems of the world.

OCCURRENCE :

It is extremely common mineral which is found throughout the world in sedimentary, metamorphic and igneous rocks. In the form of limestone and marble it makes up a significant portion of Earth's crust and serves as one of the largest carbon repositories on our planet. Calcite is a common constituent of sedimentary rocks, limestone in particular, much of which is formed from the shells of dead marine organisms. Approximately 10% of sedimentary rock is limestone. Calcite may also be found in volcanic or mantle-derived rocks such as carbonatites, kimberlites, or rarely in peridotites. Lublinite is a fibrous, efflorescent form of calcite. Calcite formed as a deposit in caves from the precipitation of calcium carbonate In India calcite is found in the states of Karnataka, Andhra Pradesh, Gujarat, Madhya Pradesh and Rajasthan.

PROPERTIES :

1. Calcite is available in many colors white, gray, yellow, green, red, blue, brown sometimes colorless.
2. On Mohs scale its hardness is determined as 3.
3. It is very brittle.
4. Specific gravity of calcite is 2.7.
5. Its streak is white and fracture is conchoidal.
6. They are transparent to translucent.
7. Calcite has refractive index varies between 1.4 to 1.6.
8. It is soluble in dilute acids.

USES :

1. Calcite is used in the construction of buildings as limestone and marble.
2. These materials are easily mixed, transported and placed in the form of slurry that will harden into a durable construction material.
3. Since calcite dissolves well in dilute acids it used in chemical industries as neutralizer.
4. They are also heated to produce lime that has a much faster reaction rate in the soil.
5. Calcite also has use in pharmaceutical industry in making medicines like in chewing tablets for neutralization of stomach acids.
6. Calcite has been used as a whitewash and it is also used as one of the inert coloring ingredients of paint.
7. Its low hardness makes it an effective cleaning agent that does not damage the surface being cleaned.
8. It is also crucial in the manufacture of fertilizers, metals, glass, rubber, and paint.
9. Calcite is also the main component of Chalk, which is processed as drawing chalk.

Question and Answers :

1.Calcite is available in what forms of rock?
Ans : Calcite found in sedimentary, metamorphic and igneous rocks.

2.What is the hardness of calcite?
Ans : Hardness of calcite is found to be 3.

3. Mention the important properties of calcite mineral?
Ans :
a. It is very brittle.
b. Specific gravity of calcite is 2.7.
c. It is soluble in dilute acids.

4.What are the uses of calcite?
Ans : a. Calcite is used in the construction of buildings as limestone and marble.
b. Calcite is used in the construction of buildings as limestone and marble.
c.Its low hardness makes it an effective cleaning agent that does not damage the surface being cleaned.

Calcite Pictures :


Calcite - Mineral Process Engineering Click Here for Larger Calcite Image


References :

www.wikipedia.com
www.galleries.com
www.mindat.com
www.mineralzone.com

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