Danburite - Encyclopedia

    Class : Silicates
    Subclass : Tectosilicates
    Crystal system : Orthorhombic
    Chemistry : CaB2(SiO4)
    Rarity : Rare

Danburite is a rare pneumatolytic mineral formed during the injection of pegmatitic magmas into limestones or dolomites. It can also have an hydrothermal origin in metalliferous veins and alpine fissures. It owes its name to its locality of discovery : Danbury, Connecticut, USA. It is generally elongated and terminated prismatic crystals reminiscent of topaz. Transparent to translucent, it is mostly colorless to white, sometimes yellow to brown, pink, or more rarely orange or purplish. The danburite is a mineral that is sometimes cut in faceted gemstones for jewelery but it is still more a stone reserved for the collection.

Danburite in the World

Large crystals of danburite are common, 50 cm colorless to white specimens are known on the Tituje deposit (Siberia) and 30 cm crystals were extracted from Dalnegorsk (Siberia). The pegmatite from Anjanabonoina (Madagascar) has produced magnificent yellowish to orange-colored crystals up to 30 cm in size and considered like the best ones in the World. The Mexican deposits have also supplied remarkable pieces with a gemmy quality : La Verde and Charcas. Mogok alluvium deposits (Myanmar) contains yellow-colored crystals often cut for jewelery. Danburite is found in less exceptional specimens in the American fields of Riverside and Ramona (California) but also in Danbury (Connecticut), which is also the type-locality. Finally, it is found in chloritic centimeter crystals in the Alpine fissures of the Swiss Graubünden (Val Medel, Mount Scopi).

Danburite in France

In France, danburite has been reported at St-Maime in the Alpes-de-Haute-Provence where it is found in pyrometamorphic rocks.

Fakes and scams

Can be easily confused with topaz especially when cut because the refractive index of these 2 species is very close.

Hardness : 7 to 7.5
Density : 2.93 to 3.02
Fracture : Subconchoidal to irregular
Trace : White

TP : Translucent to transparent
IR : 1.630 to 1636
Birefringence : 0.006
Optical character : Biaxe (+/-)
Pleochroism : None
Fluorescence : Blue to green-blue

Solubility : Hydrochloric acid

Magnetism : None
Radioactivity : None