Gwindel Quartz

Chemical formula: SiO₂

Gwindel Quartz is a rare and prized form of quartz in which crystals are twisted around an axis, forming unique, flattened aggregates.

## Characteristics Gwindel Quartz is not a separate mineral, but a specific and rare form (habit) of quartz. Its name comes from the German word "gewunden", meaning "twisted". Its characteristic feature is the visible twisting of a group of almost parallel crystals around a common axis (usually the a-axis). These crystals grow on top of each other, with each successive crystal being minimally rotated relative to the previous one, creating a spiral growth effect. The entire aggregate is often flattened perpendicular to the crystallographic c-axis, giving it a tabular or lenticular appearance. The most typical and sought-after Gwindels are composed of smoky quartz. ## Physical Properties As a variety of quartz, Gwindel possesses its basic physical properties. It has a hardness of 7 on the Mohs scale, making it a relatively scratch-resistant mineral. It has a vitreous luster on crystal faces and a conchoidal fracture. The density is approximately 2.65 g/cm³. It does not exhibit cleavage. ## Colors and Varieties The most common and highly valued form by collectors is smoky Gwindel quartz, with coloration ranging from light brown to almost black (morion). Colorless Gwindels of rock crystal (mountain crystal) also occur, and amethyst forms are much rarer. Specimens with inclusions of other minerals, most often chlorite, which gives them a greenish tint, are also found. ## History and Name The name "Gwindel" is a term historically used by Alpine crystal seekers (strahlers) and has been adopted in mineralogy. It refers directly to the twisted nature of these crystals. This form is inextricably linked to classic Alpine fissure deposits, where it has been found and described for hundreds of years. ## Applications Gwindel Quartz has no industrial applications. It is exclusively a collector's stone, highly valued for its rarity, specific aesthetics, and interesting crystallogenesis.

Properties

Mohs hardness: 7
Luster: Vitreous
Streak: White
Density: 2.65
Cleavage: None
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Trigonal

Diagnostic features

## Identification The key diagnostic feature is the visible twisting of the crystal aggregate. This effect is best observed by following the striations on the prism faces (m-type faces), which, instead of running parallel, form gentle arcs. The entire specimen is usually flattened, which distinguishes it from typical, elongated quartz crystals. ## Distinguishing from similar minerals Gwindel Quartz is sometimes confused with ordinary parallel intergrowths of quartz crystals. In the case of parallel intergrowths, the crystallographic axes of individual crystals are perfectly parallel to each other, without visible rotation. In Gwindel, there is a systematic, slight twisting of each successive crystal relative to the previous one. ## Crystal Forms The Gwindel form is an aggregate of tabular or short-prismatic quartz crystals, almost parallelly intergrown and twisted around a common axis. The degree of twisting can vary – from barely noticeable (so-called "semi-Gwindel" or "open Gwindel") to very pronounced, where the angle between the first and last crystal in the stack reaches several tens of degrees.

Geological environment

## Genesis Gwindel Quartz is a typical mineral for Alpine-type fissures. It forms under hydrothermal conditions, at relatively low temperatures and high pressures, in open fractures and fissures cutting metamorphic rocks such as gneisses and schists. The exact mechanism causing the twisting of crystals during growth is not fully understood, but it is associated with specific physicochemical conditions and pressure gradients within the fissure. ## Mineral associations Minerals typically associated with Gwindel Quartz in its natural environment are other Alpine fissure minerals: adularia (a variety of orthoclase), chlorite (often as inclusions or coatings), hematite (in the form of "iron roses"), titanite, apatite, fluorite (especially pink octahedra), and calcite. ## Localities The most famous and classic localities for Gwindel Quartz are in the Alps. The most important include: the Mont Blanc massif (on the French side, in the Chamonix area, and the Italian side), Swiss cantons of Uri (e.g., Göschenertal, Tiefenbach valleys), Valais, and Graubünden (e.g., Val Giuv). Significant specimens also come from the Polar Urals in Russia. Rarer occurrences have also been reported in Brazil and Pakistan.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of Gwindel Quartz depends on several factors. The most important is the degree and distinctness of the twist – the more visible the rotation, the more valuable the specimen. Transparency and strong luster are highly prized. For smoky quartz, an intense and evenly distributed color is desirable. Large, undamaged specimens are exceptionally rare and sought after. An additional advantage is the aesthetic combination with other associated minerals, e.g., pink fluorite or white adularia. ## Popular Localities The most valued specimens by collectors come from classic localities in the Alps. Specimens from the Mont Blanc region (France/Italy) and from Swiss valleys such as Val Giuv or Tiefengletscher are considered exemplary and fetch the highest prices on the collector's market. Russian Gwindels from the Urals, although also valued, are usually differently formed and often have a darker color.

Care and storage

## Cleaning Specimens can be safely cleaned in lukewarm water with mild soap, using a soft brush to remove dirt from crevices. After washing, they should be thoroughly rinsed, preferably in distilled water, and left to dry completely. Solid, undamaged specimens without inclusions can be cleaned in ultrasonic cleaners, but caution should be exercised. ## What to avoid Sudden temperature changes (thermal shock) should be avoided, as they can cause internal cracks. Quartz is resistant to most chemicals, with the exception of hydrofluoric acid, which etches it. Although quartz is stable, smoky varieties may slightly fade with prolonged, intense exposure to sunlight. ## Storage Gwindel quartz specimens, especially those with sharp edges and delicate terminations, should be stored separately to avoid chipping in contact with other minerals. It is best to display them in closed showcases, protecting them from dust and accidental damage.

Sources

IMA Mineral List (CNMNC)