The six crystal families are formed by combining the hexagonal and trigonal crystal systems into one hexagonal family, in order to eliminate this confusion.
12.
Hidalgoite is categorized under the trigonal crystal system and Rm space group and can be denoted by the H-M symbol ( 2 / m ).
13.
In three dimensions, the crystal families and systems are identical, except the hexagonal and trigonal crystal systems, which are combined into one hexagonal crystal family.
14.
The trigonal crystal system consists of the 5 point groups that have a single three-fold rotation axis ( see table in Crystal system # Crystal classes ).
15.
Five of the crystal systems are essentially the same as five of the lattice systems, but the hexagonal and trigonal crystal systems differ from the hexagonal and rhombohedral lattice systems.
16.
"' Sodium cyanate "'( NaOCN ) is a white crystalline solid that adopts a body centered rhombohedral crystal lattice structure ( trigonal crystal system ) at room temperature.
17.
In the trigonal ( bararite ) and hexagonal ( gamma, ? ) forms, the layers are perpendicular to the c-axis . ( Note : Trigonal crystals are part of the hexagonal group.
18.
"' Carlosruizite "'is a H 2 O . It has a low density ( specific gravity of 3.36 ), colorless to pale yellow, transparent mineral which crystallizes in the trigonal crystal system.
19.
Crystals in the rhombohedral lattice system are always in the trigonal crystal system, but some crystals such as alpha-quartz are in the trigonal crystal system but not in the rhombohedral lattice system ( alpha-quartz is in the hexagonal lattice system ).
20.
Crystals in the rhombohedral lattice system are always in the trigonal crystal system, but some crystals such as alpha-quartz are in the trigonal crystal system but not in the rhombohedral lattice system ( alpha-quartz is in the hexagonal lattice system ).
