Crandallite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated phosphates
    Crystal system : Rhombohedral
    Chemistry : CaAl3(PO4)2(OH)5 H2O
    Rarity : Common

Crandallite (formerly called pseudowavellite) is a hydrated calcium aluminum phosphate. It is an essentially secondary mineral which forms in the zone of supergene alteration of aluminous and phosphate rocks. Its formation environment is therefore broad : carbonatites and nepheline syenites, granitic pegmatites, various sedimentary rocks (including phosphorites), sometimes iron deposits. It is more rarely a primary mineral newly formed in anoxic marine sediments or clayey sediments in a tropical climate. It was named in honor of the American engineer Milan L. Crandall. Crandallite forms small prismatic crystals (1 mm maximum), or pseudocubic rhombohedra ; more commonly it is found in rosettes, spherules or nodular masses with a fibroradiated texture, sometimes in powdery crusts. Its color is yellow, white or gray, sometimes brown.

Main photo : Crandallite from Tom's Quarry, Kapunda, North Mt Lofty Ranges, Mt Lofty Ranges, Australia © Matteo Chinellato

Crandallite from Mont-des-Groseillers, Wallonia, Belgium © Scapin Giovanni
Crandallite from Tom's Quarry, Kapunda, Australia © Enrico Bonacina
Crandallite from Échassières, Allier, France © Pascal Chollet
Crandallite from Azcárate Quarry Eugui, Esteríbar, Navarre, Spain © Carlos Pareja

Crandallite in the World

Crandallite is known in many American pegmatites : Fletcher and Palermo near North Groton (New Hampshire), the famous Tip-Top and Hugo pegmatites (South Dakota), etc... Crandallite is also abundant in spectacular variscite nodules from Fairfield, Utah. Outside the United States, crandallite is also common in various contexts: pegmatite from Picui (Paraiba, Brazil), carbonatite from Mount Weld (Australia), nepheline syenite from Kovdor (Kola, Russia), phosphate iron deposit from Iron Monarch near Iron Knob (Australia), etc...

Crandallite in France

In France, crandallite is known at Échassières (Allier), at Montebras (Creuse), at La Fumade (Tarn), at Caurel (Côtes d'Armor) and in a few other deposits, it is never spectacular.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fake identified for this mineral species.


Hardness : 5
Density : 2.78 to 3.04
Fracture : Irregular
Streak : White

TP : Translucent to opaque
RI : 1.613 to 1.632
Birefringence : 0,011
Optical character : Uniaxial +
Pleochroism : None
Fluorescence : None

Solubility : Acids


Magnetism : Paramagnetic
Radioactivity : None

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