Vyuntspakhkite-(Y)

Formula: (Y,Yb)₄Al₃Si₅O₁₈(OH)₅

Origin of name: after locality Mount Vyuntspakhk, Kola Peninsula, Russia

Crystal system: Monoclinic

Crystal class: 2/m

Twinning:

Unit cell: a = 5.83, b = 14.763, c = 6.216, β = 123.05°

Colour: Colourless to tan, orange

Diaphaneity: Transparent

Luster: Adamantine

Habit: crystals slender prismatic 0.5 to 0.7 mm

Hardness:  6-7

Specific gravity: 4.02

Cleavage: None

Tenacity: Brittle

Streak: White

Synonyms/varieties:

Comments:  Faint yellow-green cathodeluminescence when rich in Y.