Rhombohedral System

Also known as trigonal, the rhombohedral system is defined by three equal axes that are equally inclined to each other at an angle other than $90^\circ$. It can be thought of as a cube stretched along its body diagonal. Lattice parameters: $a = b = c$, and angles $\alpha = \beta = \gamma \neq 90^\circ$. Examples: Quartz, Calcite, Bismuth.