Quartz Gwindel

Quartz crystals that grew along and are slightly rotated around a single a-axis. This results in twisted and tabular crystals. The twist reflects the handedness of the quartz crystals. With increasing distance from the base
- right-handed gwindels twist clockwise.
- left-handed gwindels twist counter-clockwise.
In most gwindels the handedness can easily be determined by the position of the trapezohedral "x"-faces.

Gwindels are found in alpine-type fissures and are always accompanied by macromosaic quartz of normal habit. They are often smoky; colorless "rock crystal" gwindels are less common.

The structural base of the twist has just recently been discovered: A high number of straight screw dislocations cause a uniform so-called Eshelby twist (Cordier and Heidelbach, 2013; Eshelby, 1953) that is typical for slow growing crystals. This slow growth is in line with the occurrence of gwindels in certain alpine-type fissures.

Because of the often multiple tips and the strong development of sutures on the crystal surface, gwindels are often described as lateral stacks of quartz crystals. This is not correct: each gwindel starts as a single crystal, and only the overgrowth with quartz of a macromosaic structure causes the impression of a composite specimen (Kuzmina et al, 1987; Dolino and Bastie, 2009).

Note: Nobody says "Quarzgwindel" in Switzerland or Austria, it is just "Gwindel".