ClipArt ETC
"The vertical crystallographic axis is one of trigonal symmetry, and the three horizontal crystallographic axes of binary symmetry." — Ford, 1912

Symmetry of Rhombohedral Class

"The vertical crystallographic axis is one of trigonal symmetry, and the three horizontal crystallographic…

This is a diagram of the sea-anemone, illustrating another type of radial symmetry. A, cross section; B, longitudinal section. c, the chamber between the mesenteries (m).

Sea-Anemone

This is a diagram of the sea-anemone, illustrating another type of radial symmetry. A, cross section;…

"The Sphenoidal Class corresponds in the Tetragonal system to the Tetrahedral class in the Isometric System. It is characterized by the following symmetry: The three crystallographic axes are axes of binary symmetry, and there are two vertical diagonal planes of symmetry." — Ford, 1912

Symmetry of Sphenoidal class

"The Sphenoidal Class corresponds in the Tetragonal system to the Tetrahedral class in the Isometric…

"Spherical cell (resting stage of Amoeba) illustrating general or universal symmetry. Any plane passing through the center will divide it into two essentially equal portions." — Galloway

Spherical Cell

"Spherical cell (resting stage of Amoeba) illustrating general or universal symmetry. Any plane passing…

"The symmetry of this class is as follows: The three crystallographic axes are axes of binary symmetry; the four diagonal axes are axes of trigonal symmetry; there are six diagonal planes of symmetry." — Ford, 1912

Symmetry of tetrahedral class

"The symmetry of this class is as follows: The three crystallographic axes are axes of binary symmetry;…

This figure shows two tetrahedrons with parallel axes, and symmetrically placed with reference to the faces of the cube. The example given is a tetrahedrite crystal.

Tetrahedrite

This figure shows two tetrahedrons with parallel axes, and symmetrically placed with reference to the…