Ussingite
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Ussingite is a silicate mineral with formula Na₂AlSi₃O₈.
It was named for Niels Viggo Ussing, Copenhagen, Denmark. Wikipedia
Color: pale to medium violet, reddish violet; sometimes barely tinted purple
Crystal class: Pinacoidal (1); (same H-M symbol)
Crystal system: Triclinic
Mohs scale hardness: 6–7