From granites to pegmatites

This project focuses on important steps in the resolution of fundamental questions regarding pegmatite-forming media and processes, including:

  • water concentration in real pegmatite melts,
  • separation from the granitic host, as critical step,
  • melt-melt-fluid immiscibility,
  • main and trace element distribution in different melt and fluid phases,
  • extreme enrichment of water, alkalis and boron and its consequences,
  • significance of the high-temperature sol-gel state, especially during the formation of the quartz core.

An important tool in this intricate task are the fluid and melt inclusions in minerals as media for the deciphering mineral-forming processes, constraining the temperature, pressure and the compositions of the long-gone fluids which were actively involved in the different mineral-forming environments during pegmatite formation. Thus, studies of melt and fluid inclusions provide the critical evidence for liquid compositions and phase relations in nature. Our philosophy for further progress in this field is always to combine natural observations, including the inclusion research, with experimental and analytical studies of key subsystems.

Fig. 1:  Malkhan pegmatite (Transbaikalia, Russia): An boron and water-rich melt inclusion in quartz from the graphic zone [Bulk: ~10.7 % (g/g) H3BO3 and 25.6 % (g/g) H2O]
Fig. 2: Extreme enrichment of B and Cs during pegmatite-forming processes, visualized by daughter crystals in fluid inclusions. G – silicate glass, S – water-rich solution, V – vapor, H3BO3 – sassolite
Fig. 3: Solubility of ramanite-Cs daughter crystals in fluid inclusions in pegmatite minerals vs. the melting temperature (tS)


Rainer Thomas
Dr. Rainer Thomas
Chemistry and Physics of Earth Materials
Building D, Room 320
14473 Potsdam
+49 331 288-1478