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Epidote minerals are known since the 18th century, but at that time the greenish to dark colored varieties were termed actinolite or schorl and not distinguished from the minerals to which these names apply today. Haüy defined the mineral species and introduced the name “epidote” in 1801, whereas Werner in 1805 used the term pistacite (quoted from Hintze 1897). Epidote is derived from greek epidosis = to increase, because the base of the rhombohedral prism has one side larger than the other and pistacite refers to its green color (all references for names after Lüschen 1979; Blackburn and Dennen 1997). Weinschenk (1896) proposed the name clinozoisite from its monoclinic symmetry and zoisite-like composition for those monoclinic members of the epidote family that are Fe poor, optically positive and have low refractive indices and birefringence.
Zoisite was probably confused with tremolite until the beginning of the 19th century. In 1804, Siegmund Zois, Baron von Edelstein 1747–1819, an Austrian sponsor of mineral collections, found and described a new mineral in a handspecimen from the Saualpe Mountains in Carinthia that was named zoisite by Werner.
Haüy (1822) interpreted zoisite as a variety of epidote and included it in his “epidote spezies.” Weiss (1820) presented a theory of the epidote system and also discussed crystal morphological features of the epidote minerals (Weiss 1828). Rammelsberg (1856) studied the relationship between epidote and zoisite and presented a compilation of chemical analyses of zoisite. He already noticed that the relative concentrations of di-, tri- and tetravalent cations are identical in zoisite and epidote but that the Fe content in zoisite (about 2–3.5 wt% Fe2O3) is generally less than in epidote (about 9–12 wt% Fe2O3). Piemontite (see Bonazzi and Menchetti 2004) was probably first described in 1758 by Cronstedt …