Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Paul Rustemeyer

Tourmaline Crystals with Corrosion Phenomena from the Skardu Area, North Pakistan. Part 2: Inner Morphology of Tourmaline crystals with corrosion and subsequent healing

Journal of Geosciences, volume 71 (2026), issue 1, 79 - 99

DOI: http://doi.org/10.3190/jgeosci.0055.25

From several hundred dark tourmaline crystals from Skardu, Pakistan, stacks of tourmaline thin sections perpendicular to the c-axis (“cross-cuts”) were prepared. In contrast to standard methods, the thickness of the slices was adjusted to their optical density, as they have been ground thin until the colour zoning became visible and colour depth reached its optimum. Some of these outwardly inconspicuous tourmaline crystals show quite complex corrosion patterns in their cross-cuts. The images of the stacks of thin section deliver for each position in the crystal information about the morphology of the original crystals, the usually complex contours of the corroded crystal and the stages of growth on the way to the healed crystal. With this morphological information from the stacks of cross-cuts profiles of the crystals parallel to the c-axis were derived, which then allowed to reconstruct simplified growth histories of the tourmaline crystals.
The examples show that corrosion may take place during early, intermediate, and late stages of tourmaline growth. Some crystals exhibit even two corrosion and subsequent healing episodes. Twelve examples of such crystals are presented, illustrating the diversity and different intensity of corroded and healed tourmaline. This inner architecture of crystals is a good recorder of the discontinuous growth and dissolution history of tourmaline, giving valuable information on the sequence and intensity of supersaturated and undersaturated, corrosive fluids in the crystallizing pegmatite pocket.