Ussingite

Ussingite is a silicate mineral with formula Na₂AlSi₃O₈(OH).^[4]

Ussingite
Ussingite from Shkatulka pegmatite, Umbozero mine (Umbozerskii mine), Alluaiv Mt, Lovozero Massif, Kola Peninsula, Murmanskaja Oblast', Northern Region, Russia
General
Category	Phyllosilicate minerals
Formula	Na2AlSi3O8OH
IMA symbol	Usg[1]
Strunz classification	9.EH.20
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Identification
Color	pale to medium violet, reddish violet; sometimes barely tinted purple
Fracture	irregular/ uneven
Tenacity	brittle
Mohs scale hardness	6–7
Luster	sub-vitreous
Streak	white
Diaphaneity	transparent, translucent
References	[2][3]

It was named for Niels Viggo Ussing (1864–1911), Copenhagen, Denmark.