Kristallstrimmor

Kristallstrimmor are a geological phenomenon described as elongated, ribbon-like aggregates of crystals that form linear features within host minerals or rocks. The term, from Swedish roots meaning crystal streaks, denotes crystal growth patterns that align along specific directions, producing visible streak-like bands that record crystallization history and fluid movement.

Formation and distribution

Kristallstrimmor form during crystallization from melts or hydrothermal fluids under temperature and concentration gradients. Directional cooling or confined spaces promote anisotropic crystal growth, leading to slender, streak-like crystals that can cross-cut or align with existing textures. They are commonly reported in association with quartz, calcite, feldspar, and other framework minerals, and may appear in granitoids, pegmatites, or metamorphic rocks.

Morphology and appearance

The streaks vary from translucent to transparent and range in width from tens of micrometres to a few millimetres. They can be colorless or pale and may align with the rock’s foliation or bedding. In some cases, kristallstrimmor preserve growth zoning or compositional changes within the crystal lattice, providing a record of the mineral’s crystallization environment.

Significance and interpretation

In petrography, kristallstrimmor are used to infer directional growth, fluid flow, and differential stress during formation. Their patterns help distinguish growth fronts from post-crystallization deformation and can indicate the thermal and chemical history of a rock.

Methods and terminology

Investigation relies on petrographic microscopy, scanning electron microscopy, X-ray diffraction, and cathodoluminescence to resolve growth features and zoning. The concept is distinct from the mineral streak used in ore testing and from crystal twinning or other growth textures.

See also: mineralogy, crystal growth, hydrothermal processes.