Lazulite - Encyclopedia

Lazulite crystals from Canada

    Class : Phosphates, arsenates, vanadates
    Subclass : Anhydrous phosphates
    Crystal system : Monoclinic
    Chemistry : MgAl2(PO4)2(OH)2
    Rarity : Uncommon to rare


Lazulite is a metamorphic mineral from aluminous rocks rich in silica (quartzites), associated with kyanite and rutile. It is also a hydrothermal mineral from high temperature veins and pegmatites. By replacing Mg with Fe, it forms a complete solid solution which extends to the scorzalite pole. Its name comes from the Latin lazulum, the Arabic lazaward and azul, the Persian lashward (blue) and the Greek lithos (the stone). The rare crystals are acute bipyramid specimens, but lazulite usually occurs in microgrenous masses of decimetric size at most. Translucent or opaque, its beautiful deep blue color, sometimes bluish white to azure blue, is characteristic. It is a mineral which can sometimes be used as a gemstone but which is nevertheless rather reserved for the mineral collection.

Lazulite crystals from Canada

Lazulite crystals from
Rapid Creek, Yukon, Canada

Lazulite crystals from Canada

Lazulite crystals from
Rapid Creek, Yukon, Canada

Lazulite crystals from Canada

Lazulite crystals from
Rapid Creek, Yukon, Canada

Lazulite crystals from Canada

Lazulite crystals from
Rapid Creek, Yukon, Canada

Lazulite in the World

The best lazulite crystals come from a siderite vein at Cross-Cut Creek (Yukon, Canada) : 2 cm shiny crystals, midnight blue, in geodes of quartz and siderite. Quartzites from Grave Mountains (Georgia) produced bipyramid crystals with dull faces, while Werfen (Austria) shows crystals embedded in quartz and calcite. Large crystals (almost 15 cm) but of poor quality are known in Halsjöberg (Sweden). The Zermatt region (Switzerland) also has good crystals.

Lazulite in France

In France, lazulite has been described in microcrystals in the pegmatites of the Albères massif.

Twinning

Twinning Lazulite from Grave Mountains, USA

Common twin on {100}, lamellar or sometimes polysynthetic with generally a reentrant angle ; rare on {223}, by reflection on {-221}. Also reported on {210} and {021}.


On the right an 8.8 mm twin specimen from Grave Mountains, Georgia, USA. Photo © 2015 Jason B. Smith.

Fakes and treatments

There are no fakes for this mineral species. However, confusion between lazulite and lazurite (one of the minerals making lapis lazuli) is common. This confusion stems from the fact that the "L" and "R" are pronounced the same in Asia. Asian sellers are therefore particularly inclined to confuse the two species.



Hardness : 5.5 to 6
Density : 3.12 to 3.24
Fracture : Irregular
Trace : White




TP : Transparent to opaque
RI : 1.604 to 1.663
Birefringence :  0.035
Optical character : Biaxial -
Pleochroism : Strong
Fluorescence : None


Solubility : Acids

Magnetism : None
Radioactivity : None