Allanite-(Sm)

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Formula: (CaSm)(AlAlFe²⁺)O[Si₂O₇][SiO₄](OH) (Mindat formula)
Sorosilicate (Si₂O₇ groups), allanite group, epidote supergroup, samarium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.842 calculated
Hardness: 5
Streak: White
Colour: Yellowish brown
Environments

Pegmatites
Hydrothermal environments

Allanite-(Sm) is a new mineral, approved in 2024 and to date (February 2025) reported only from the type locality.

Localities

At the type locality, the Jordanów serpentinite quarry, Gmina Jordanów Śląski, Wrocław County, Lower Silesian Voivodeship, Poland, allanite-(Sm), the third samarium mineral to be discovered, was found in a granitic pegmatite in the serpentinite quarry. It occurs as subhedral to anhedral crystals with sizes of up to ~150 μm accompanied by allanite-(Nd), allanite-(Y), clinozoisite, hingganite-(Y) and xenotime-(Y). Allanite-(Sm) is yellowish brown with a white streak and a vitreous lustre. It is brittle, with conchoidal fracture and imperfect cleavage.
Allanite-(Sm) and the associated allanite-(Y), allanite-(Nd) and hingganite-(Y) are secondary minerals precipitated from calcium-rich hydrothermal fluid during the metasomatic alteration of the pegmatite. They accumulated rare earth elements released by the alteration of nearby xenotime-(Y) (AM Research Article| September 20, 2024).

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