MCKELVEYITE

    Class : Carbonates, nitrates, borates
    Subclass : Hydrated carbonates
    Crystal system : Triclinic
    Chemistry : Ba3Na(Ca,U)(Y,Nd)(CO3)6 3H2O
    Rarity : Very rare

Mckelveyite is a group of two carbonates, from nepheline syenites and carbonatites, which form a series between the yttrium pole mckelveyite-(Y) and the neodymium pole mckelveyite-(Nd). Its name was given in honor of Vincent Ellis McKelvey, Director of the US Geological Survey. We know relatively little about this extremely rare mineral ; it forms small pseudohexagonal crystals in barrels of 3 cm maximum, and pseudorhombohedral discoid crystals of 3 mm in veins of calcite and natrolite. Its crystals can also be lamellar. Its colors vary : white, green, gray of different tones, yellow to brown, sometimes black.

Main photo : Mcguinnessite from Lobminggraben, Styria, Austria © Christian Auer

Mckelveyite in the World

Mckelveyite is known in the nepheline syenite of Khibiny (Kola, Russia), as well as in the carbonatites of its surroundings (Sallanlatvi and Vuoriyarvi) but also at Mont St-Hilaire (Canada). It is also found in 0.5 mm lamellar aggregates at Green River (Wyoming).

Right photo : Mckelveyite-(Y) from Poudrette Quarry, Mont St-Hilaire, Quebec, Canada © Jerry Cone


Mckelveyite in France

Mckelveyite is not known in the French underground.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 3.5 to 4
Density : 3.25
Fracture : Irregular
Streak : White

TP : Transparent to opaque
RI : 1.550 to 1.658
Birefringence : 0.099 to 0.104
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : None

Solubility : -

Magnetism : NoneRadioactivity : Medium