Thermal behavior of schorl up to breakdown temperature at room pressure


  • Beatrice Celata Sapienza University of Rome
  • Paolo Ballirano Sapienza University of Rome
  • Ferdinando Bosi Sapienza University of Rome
  • Giovanni Battista Andreozzi Sapienza University of Rome
  • Christopher Beckett-Brown Geological Survey of Canada




 Schorl is one of the most widespread tourmaline compositions in the world, known from many different geological settings. Its role as boron and water carrier has been moderately investigated together with its stability field. In this study, the richest schorl in Fe2+ content was investigated to constraint its breakdown temperature at room pressure through in situ powder X-Ray Diffraction (in situ pXRD), its breakdown products and the coupled thermally induced dehydrogenation-dehydrogenation process experienced approaching the breakdown conditions. 
Schorl turned out to begin its breakdown at 850 °C with the first appearance of hematite, followed by a dominant B-mullite phase. The breakdown reaction of schorl can be expressed as follows: 2NaFe2+3Al6(BO3)3Si6O18(OH)=3Fe2O3+4/3Al9Si2BO19+(Na- Si- B-rich) glass+4H2O. 
The breakdown process is completed at 950 °C, when no trace of residual tourmaline is found. Annealing the schorl at 450 °C in air was enough to set the Fe oxidation out, counterbalanced by the deprotonation reaction: (Fe2+)+(OH)- → (Fe3+)+ (O2-)+1/2H2(g). 

Author Biographies

Paolo Ballirano, Sapienza University of Rome

Graduated in Geological Sciences at the University of Rome "la Sapienza" in 1990, PhD in Earth Sciences in 1994, Researcher from March 1999 at the Department of Earth Sciences (DST), University of Rome "la Sapienza", from January 2005 Associate Professor and since November 2016, Full Professor at DST. He has been member of several committees, panels, commissions acting at the University of Roma “La Sapienza”, some of them elective, with governing, managing and organizing function. Head of the Department of Earth Sciences of Sapienza from November 1, 2016 to October 31, 2019, he has authored ca. 250 among articles, chapters and congress communications. He has been member of both the Organizing and Scientific Committee of several congresses, schools and meetings.

Ferdinando Bosi, Sapienza University of Rome

Ferdinando Bosi received his PhD from Sapienza Rome University in 2001. He was a post-doctoral researcher first at Sapienza University and later at the Swedish Museum of Natural History (Stockholm, Sweden). He returned to Rome in 2008 to take up an academic position at the Department of Earth Sciences (Sapienza University) where he currently works as a professor/researcher of mineralogy and crystallography. Since 2010, he is the leader of the single-crystal X-ray diffraction laboratory, Sapienza University. Bosi's main research focuses on systematic and crystal-chemical aspects of minerals from an experimental and theoretical viewpoint. For his work on tourmalines and spinels, the mineral bosiite was named after him in 2015. From April 2021 to September 2022, Bosi was a member of the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA). In October 2022, he was appointed as CNMNC Chair.

Giovanni Battista Andreozzi, Sapienza University of Rome

Graduated in Geological Sciences at the University of Rome "la Sapienza" in 1993, PhD in Earth Sciences in 1997, post-doc at the Department of Mineralogy, Natural History Museum, Stockholm, and then at the Department of Mineralogy and Petrology, University of Padova. He got the position of permanent researcher in Mineralogy in 2000 at the Department of Earth Sciences (DST), Sapienza University of Rome, and the position of Associate Professor in 2012. Since 2021 is winner of a position as Full Professor at DST. At DST, he is responsible of the laboratories of Mössbauer spectroscopy and of Experimental mineralogy. In Sapienza, he served as Coordinator of the PhD in Earth Sciences from 2012 to 2018 and Director of the PhD School in Sciences from 2017 to 2018, and he has been member of several commissions and panels with managing and organizational roles.
Since 2018 is member of the Executive board of the Italian Society of Mineralogy and Petrology (SIMP) and delegate in the European Journal of Mineralogy (EJM) Managing Committee. Since 2000 is reviewer for the highest-ranking international journals in Mineralogy and Materials Sciences. Since 2010 served as Expert Evaluator of research projects for the Italian Ministry of University and Research, for several national research agencies at European level, and for the Research Executive Agency - European Union (REA-EU), Marie Curie calls, panel Environment, FP7 and H2020 programmes. He was Visiting Professor in 2001, 2003 and 2007 at the Department of Mineralogy, Swedish Museum of Natural History, Stockholm, and in 2018 at the Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Sorbonne Université, Paris. He has been organizer and co-chairman of ECMS 2015 (8th European Conference on Mineralogy and Spectroscopy, Rome 2015), and of TUR2021 (3rd International Conference on Tourmaline, Elba Island, 9-11 September 2021).
The research activity is focused on minerals and their synthetic analogues with the aim of developing interpretation models able to clarify the relationships among a) genetic conditions (P, T, X, fO2, etc.), b) crystal structure, crystal chemistry and cation distribution, c) associate physical properties, and d) potential applications in Earth Sciences, Planetary Sciences, Environmental Sciences, Materials Sciences, and Gemology. Results have been presented in the most relevant conferences in the field and are published in highest-ranking international journals.