Formula: Y₂Fe²⁺Be₂Si₂O₁₀ Often slightly radioactive due to minor U and/or Th contents; therefore often metamict.

Species:

Colour: Black, greenish-black, brown

Lustre: Vitreous, Greasy

Hardness: 6½ – 7

Specific Gravity: 4.36 – 4.77

Crystal System: Monoclinic

Member of: Gadolinite Subgroup > Gadolinite Group > Gadolinite Supergroup

Name: Named in honor of Johan Gadolin (1760-1852), chemist, physicist, and mineralogist. He discovered what would be the element yttrium, the first rare earth discovered. The “-(Y)” suffix was added in 1987 and is for to the predominance of yttrium as the REE in the composition.

Type Locality: Ytterby, Resarö, Vaxholm, Stockholm County – Sweden

The yttrium analogue of gadolinite-(Ce) and Gadolinite-(Nd). Difficult to distinguish from hingganite-(Y).