What is the monoclinic crystal system in mineralogy ?

Monoclinic crystal system : definition

The monoclinic system is a crystalline system whose unit cell is an oblique prism with four parallelogrammatic side faces equal to 2 to 2, and two rectangular bases. The three axes are of different lengths and only two angles are equal to 90° ; the third is variable and characteristic of the mineral species. This system has 3 crystalline classes.

This system include about 21% of mineral species, the most common being micas, the majority of amphiboles and pyroxenes, gypsum, orthoclase, talc, chlorites, etc...

Certain monoclinic cells are said to be pseudocubic, pseudoquadratic, pseudo-orthorhombic or pseudohexagonal, when the cell parameters of a given monoclinic crystal approach those of these crystalline systems.

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