Dark Blue Aquamarine form the True Blue Showing, Yukon Territory

ABSTRACT

Dark blue aquamarine was discovered in the Yukon Territory in 2003.  The crystals occur in a swarm of quartz ± siderite ± fluorite ± allanite veins that fill tension gashes in a syenite stock.  Previous studies suggest a metamorphic origin for the mineralizing fluid and local derivation of vein constituents.  The dark blue beryl contains nearly 6.0 wt.% FeO and the colour is thought to be due to intervalence charge-transfer between Fe²⁺ and Fe³⁺ cations.  Five stones weighing up to 0.82 carats were faceted in 2003, but these are heavily fractured and included.  However, many of the smaller crystals discovered to date are transparent.