Pinkish crystal aggregates of the rare arsenate mineral adelite from the famous Franklin deposit (Sterling Hill, Ogdensburg, Sussex County, New Jersey, United States of America). — Photo: David Hospital · CC BY-SA 4.0
Adelite
A rare calcium-magnesium arsenate that swaps partners freely with related minerals in the adelite–duftite group.
Intro adapted from Wikipedia (CC BY-SA).
Adelite is an IMA-recognized mineral species in the arsenate class, with the chemical formula CaMg(AsO₄)(OH).
It crystallizes in the orthorhombic crystal system (space group P2_12_12_1). It is a member of the Adelite structural group.
Key properties: Mohs hardness 5; specific gravity 3.71–3.76; Resinous luster; optically biaxial.
IMA symbol Ade, grandfathered status — known before the IMA’s founding, named in 1891.
A rare mineral found in a metamorphosed Fe–Mn orebody (Långban, Sweden); on willemite-franklinite ore from a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA).
It is found associated with Sarkinite, arsenoclasite, braunite, hedyphane, fredrikssonite (Långban, Sweden); hausmannite, magnetite, copper (Kittel mine, Sweden); hodgkinsonite, barite.
Its name comes from the Greek for indistinct, as it typically lacks transparency.