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The mineral calcite
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CALCITE（方解石）is one of the most common minerals on the earth. It occurs in a seemingly unlimited variety of shapes and colours. It constitutes a major portion of many of the earth's rocks.
Calcite and aragonite (文石）are polymorphous (多晶形的). Although calcite and aragonite contain the same elements, they differ in crystal structure. Calcite forms trigonal (三棱或三角的) crystals, whereas aragonite forms orthorhombic (斜方晶的或正晶的) crystals. Sometimes, the crystals of calcite and aragonite are too small to be detected, and it is only possible to distinguish these two minerals by complex scientific tests. Since the true identity of these forms is not known, they are simply labelled as calcium carbonate (碳酸钙). This definition accurately includes both calcite and aragonite.
Calcite exists in the form of stalagmites (石笋), and stalactites（钟乳石）.
Calcite is the primary ore of calcium (钙). It is indispensable (必不可少的) in the construction industry, forming the base of cement (水泥). Many important chemicals are created from calcite. It is also crucial in the manufacture of fertilizers, metals, glass, rubber, and paint.
The transparent Iceland spar (双折射透明方解石，又名冰洲石) variety, in which the double refraction is very apparent, is used as prisms (棱柱) for polarizing microscopes (偏光显微镜）and other optical devices.
Calcite forms rocks that are used for ornamental purposes, such as marble (大理石). Calcite is also the main component of chalk, which is processed as drawing chalk. To collectors, calcite is one of the best-known and most extensively collected minerals.
The original Iceland spar variety came from a large deposit in Iceland, as its name suggests. Currently, most Iceland spar comes from numerous places in Mexico, where it is found in great abundance. Large, golden-yellow to brown crystals have come from numerous areas in the tri-state mineral region of Kansas, Missouri, and Oklahoma in the United States.
(SD-Agencies)
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