Hambergite is a mineral with a hardness of 8 out of 10 on the Mohs scale of mineral hardness [?]. These Orthorhomibicly structured gems are made of beryllium hydroxyborate, their full chemical compound being Be2(OH)BO3.
Hambergite is a beryllium borate mineral in the classification of Nitrates, Carbonates, and Borates and is an extremely rare gemstone.
It occurs as transparent colourless orthorhombic prismatic crystals which are usually well crystallized, sometimes twinned. Its colors range to white, white grayish, and yellowish white.
Crystals are striated along the prisms. It is very hard and has one direction of perfect cleavage. It has a vitreous luster and resembles glass or quartz when cut. It has strong birefringence, much higher than zircon, and can take a good polishing.
Hambergite occurs as a rare accessory mineral in granite pegmatites with beryllium, and in alluvial gem deposits. It is associated with danburite, spodumene, apatite, beryl, feldspar, fluorite, zircon, quartz. These are found in Kashmir (India), Madagascar, the Czech Republic, Romania, USA, and Norway. Ornamental quality material usually comes from Anjanabanoana, Madagascar.
Hambergite is named after a Swedish mineralogist Axel Hamberg.
Hambergite has the lowest density of any gem with high birefringence, meaning a bigger stone will not carry a lot of weight, but will still have the play of light that one would expect from uniaxial birefringent materials such as calcite, quartz or zircon (which all have high density).