Dark Blue Aquamarine from 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.% iron oxide and the colour is thought to be due to intervalence charge-transfer between Fe^(2+) and Fe^(3+) cations. Five stones weighing up to 0.82 carat were faceted in 2003, but these are heavily fractured and included. However, many of the smaller crystals discovered to date are transparent.