The crystal structure consists of sheets stacked along the c axis.

The a and c axes lie in a plane.

The a and c axis both lie on the glide plane of symmetry.

The X sites are sandwiched between the units along the c axis.

It is common for the faces to striated parallel to the c axis (Neiva, 2008).

Crystals are short prismatic parallel to the c axis and often acicular.

The c axis of the unit cell is 0.87 nm.

The a and c axes make an oblique shape.

Cleavage is good perpendicular to the c axis, and twinning is common.

Along the c axis, normal conductivity is 10 times smaller than in the a-b plane.