castellite · noun1
From Castelli + -ite, from the surname of its discoverer, Herr Bergverwalter Castelli.
Castellite · noun2
Possibly from a very brief 19th-century Mormon settlement in Castell, Texas, which, like all Mormon communities, sent out missionaries. Identifying "Utah" as the source of the Castellite missionaries in the quote below may have been based on the common contemporaneous assumption that all Mormons were based in Utah.
Etymology from Wiktionary, CC BY-SA 4.0.