aeschynite

Aeschynite is a rare-earth niobate mineral of the oxide class that occurs in igneous and hydrothermal rocks. It has two commonly recognized varieties named for the dominant rare-earth element: aeschynite-(Ce) and aeschynite-(Y). The mineral occurs as prismatic to acicular crystals and as granular to massive aggregates. It typically presents a dark brown to black color with a metallic to submetallic luster.

In composition, aeschynite contains niobium and tantalum together with rare-earth elements; the precise chemistry varies through solid solution among niobate and tantalate components and REE substitutions. The two varieties differ in dominant REE, with Ce or Y leading. The mineral is dense and brittle.

Geologically, aeschynite forms in oxidized portions of rare-element-rich pegmatites and in hydrothermal veins associated with granitic rocks. It is commonly found with other complex oxide minerals such as titanates and uranates, and can occur in cavities and fractures where high-temperature fluids cooled.

Because of its rarity, aeschynite is mainly of interest to mineral collectors and researchers studying REE-bearing oxide minerals. It has no known significant industrial use, but its occurrence helps illuminate pegmatitic processes and REE mineralization.