Monoclinic
Euclase is a beryllium-aluminum nesosilicate prized for its rare gem-grade aquamarine-blue crystals. The name (Greek “eu-klasis”, easy to break) reflects its perfect prismatic cleavage that makes faceted euclase a connoisseur’s gem rarely seen outside specialist collections.
Occurrence
Premier sources: Ouro Preto and Capão (Minas Gerais, Brazil) for sky-blue gem crystals; Last Hope Mine (Zimbabwe) for the deepest blue color; Russia and Pakistan for additional material.
Identification
Sky-blue color + perfect lateral cleavage + monoclinic prismatic crystals + association with quartz/beryl in pegmatites or alpine clefts. Distinguish from aquamarine (beryl, hexagonal, no perfect cleavage).
Collector Notes
Brazilian sky-blue euclase from Ouro Preto is among the most coveted of all gem rarities. The cleavage makes faceting tricky — euclase gems are connoisseur targets.