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In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic system. They form a parallelogram prism . Hence two pairs of vectors are perpendicular (meet at right angles), while the third pair makes an angle other than 90°.
Crystal systems that have space groups assigned to a common lattice system are combined into a crystal family. The seven crystal systems are triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, and cubic. Informally, two crystals are in the same crystal system if they have similar symmetries (though there are many exceptions).
A crystal system is a set of point groups in which the point groups themselves and their corresponding space groups are assigned to a lattice system. Of the 32 point groups that exist in three dimensions, most are assigned to only one lattice system, in which case the crystal system and lattice system both have the same name.
The 73 symmorphic space groups can be obtained as combination of Bravais lattices with corresponding point group. These groups contain the same symmetry elements as the corresponding point groups, for example, the space groups P4/mmm (, 36s) and I4/mmm (, 37s).
2V angle: Measured: 18°–42° (low); ... Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures.
The mineral crystallises in the monoclinic crystal system. Most sources [3] [4] [5] put it in the prismatic class 2/m, with space group P2 1 /m, but Webmin [2] puts it in the sphenoidal class 2 with space group P2 1. The structure is similar to that of dolomite, but with two crystallographically different CO 3 groups. [3]
Crystal system Molecules per unit cell Lattice parameters (nm) Lattice angles (°) a b c Monoclinic [7] 4 0.850–0.868 0.487–0.508 0.922–0.974 92.8–94.5
Furthermore, the angles between two of the axes is 90° while the other angle is less than 90°. [8] Monoclinic minerals contain a twofold rotation axis where they can be rotated 360° and have the crystal face repeat every 180°. They also have the characteristic mirror plane, which can produce a perfect mirror image when divided in two.