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 1: Diversity of the outer Morphology

Journal of Geosciences, volume 71 (2026), issue 1, 57 - 77

DOI: http://doi.org/10.3190/jgeosci.0056.25

Innumerable dark tourmaline crystals from pockets in pegmatites around Skardu in Northern Pakistan have entered the mineral market as by-products of the trade of rare gem minerals. The author has searched this material for 40 years and thus found a great diversity of external and internal corrosion phenomena. Numerous crystals exhibit etch pits, hillocks, typical examples of which are presented from different types of crystal faces. Very special are regular linear etch grooves forming a trigonal pattern on the Pedion face and a checkerboard pattern on the adjacent trigonal pyramid face. A second group of tourmaline crystals exhibit more extreme dissolution phenomena, from crystals with a selectively dissolved pyramidal core zone, deeply etched faces with small remnants of the original external faces to the extreme of dissolving bodies. The observations of strongly corroded crystals support the model of an initially tourmaline-undersaturated hydrous fluid that separated from the pegmatite melt. The mechanisms of the formation of various etched morphologies on the tourmaline crystals as well as form-specific corrosion rates are discussed.
This part of the morphological study is the basis for the second part, in which similar corroded crystals are found as fossil complex color zones within outwardly perfect tourmaline crystals.