This is the blue rhodusite pebble (magnesioriebeckite). Dimensions: 2.4 x 1.3 x 1.1″ (6 x 3.4 x 2.7cm). Weight – 2.5oz (70 grams). Origin: Russia, Khakassia.
Some information about rhodusite:
Magnesioriebeckite is named for its composition containing magnesium and its relationship to Riebeckite. Riebeckite is named for famous eighteenth century German explorer and mineralogist, Emil Riebeck (1853-1885).
Magnesioriebeckite is a very rare gem that is not well know in the gem market. It is also known as Rhodusite. Magnesioriebeckite is usually found as fibrous «asbestiform» masses but a few sources produce solid, opaque, prismatic crystals of light to dark blue that can be used to create attractive cabochons.
Magnesioriebeckite may have originally been discovered by C. Palache in 1928 at the mines at Franklin, New Jersey, USA, but was incorrectly identified as Crocidolite. The year of discovery is noted as 1949 from the type locality of Alto Chapare District, Chapare Province, Bolivia.