Many studies have shown that geological processes, such as metamorphism and metasomatism, consist of multiple superimposed events developing over various timescales, with each stage overprinting the previous one and thus complicating reconstruction of the complete history. Here, we report the use of a natural calcium aluminum borosilicate mineral axinite-(Fe) [(Ca 2 Fe 2+ Al 2 BSi 4 O 15 (OH)], which occurs in skarn deposits,...