a. In crystallography, a symmetrically unique reference vector, oriented
vertically by convention. In the monoclinic system, the second setting orients
the c axis at the nonorthogonal angle beta to the unique b axis, the diad. In
the triclinic system, all axes are unique with the c axis designated by
convention. CF: a axis; b axis.
b.
One of three orthogonal reference axes, a, b, and c that are used in structural
geology.
c. To help describe the geometry of a fabric that possesses monoclinic
symmetry, the c axis lies in the unique symmetry plane at right angles to a
prominent fabric plane; thus in many tectonites the c axis is normal to the
schistosity.
d. In a kinematic sense, to describe a deformation plan that
possesses monoclinic symmetry, such as a progressive shear. Here the c axis
lies in the unique symmetry plane and normal to the movement plane. In a
progressive simple shear, the c axis lies normal to the shear plane. Syn:
c direction
Source:
Dictionary of Mining, Mineral, and Related Terms
