- © The Mineralogical Society Of America
One of the most striking features of epidote minerals is their ability to incorporate significant amounts of geochemically important trace elements such as large ion lithophile elements (LILE), especially Sr and Pb, transition metals, actinides, and rare earth elements (REE). Epidote minerals are common in a broad range of whole rock compositions and they can be the most important reservoir for these elements in a variety of crustal rocks. We summarize the available trace element data of epidote minerals including zoisite from the literature and discuss their geochemical significance. Additionally, we present a set of new data from a wide range of geological environments.
We focus on the orthorhombic polymorph zoisite [Ca2Al3Si3O11O(OH)], which shows a very limited variation in major element chemistry, and the monoclinic epidote minerals along the join Ca2Al3Si3O11O(OH)–Ca2Fe3+3Si3O11O(OH), which is typically constrained to the Al-rich part, i.e., the Fe3+ content rarely exceeds one cation per formula unit (pfu). The term “trace element” is problematic and ambiguous for the epidote minerals because they form solid solutions with actual end members whose components are usually abundant only as minor or trace elements, such as
hancockite CaPbAl2 (Al, Fe3+)Si3O11O(OH),
dollaseite CaREEAl2MgSi …