holohedron

A student examines a holohedron crystal model in geology class.

Definition

1. Noun (Crystallography):
   • A holohedron is a crystal form that possesses the highest possible symmetry for its crystal system, meaning it exhibits all the symmetry elements (such as axes, planes, and centers of symmetry) allowed by that system. In simpler terms, it is a crystal shape that is fully symmetrical, with all faces equally developed.

Usage Examples

• (Galena forms a fully symmetrical cube, the highest symmetry for the cubic system.)
• (Holohedron vs. half-symmetry form.)

Advanced Usage

• "holohedral class": a classification of crystals where the form is a holohedron.

  • The holohedral class of the isometric system includes cubes and octahedra. (Crystals in this class display full symmetry.)

• "holohedral symmetry": refers to the complete set of symmetry operations for a given crystal system.

  • Quartz belongs to the trigonal system, but its holohedral symmetry is rare in natural samples. (Full trigonal symmetry is uncommon.)

Variants and Related Words

• Holohedral (adj): relating to or having the nature of a holohedron.

  • The holohedral crystal exhibited all possible faces. (The crystal showed full symmetry.)

• Hemihedron (n): a crystal form with half the symmetry elements of a holohedron.

  • A hemihedron is a less symmetrical counterpart of a holohedron. (Half-symmetry form.)

Synonyms

• Full-symmetry form: a crystal shape with all symmetry elements.
• Complete crystal: a crystal with all faces equally developed.

Related Idioms

• None commonly used, as "holohedron" is a highly technical term in crystallography.