Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells - Dust growth in outflows from supergiantsHans-Peter Gail, Akemi Tamanai, Annemarie Pucci and Ralf DohmenA&A, 644 (2020) A139DOI: https://doi.org/10.1051/0004-6361/202038090