MONTGOMERYITE

    Class : Phosphates, arsenates, vanadates
    Subclass : Hydrated phosphates
    Crystal system : Monoclinic
    Chemistry : Ca4MgAl4(PO4)6(OH)4 12H2O
    Rarity : Uncommon

Montgomeryite is a secondary phosphate which forms at the end of the oxidation sequence of phosphate nodules in granitic pegmatites and phosphate sedimentary formations : its genesis therefore requires extensive oxidizing conditions. It was named in honor of Professor of Mineralogy, Arthur Montgomery, who was the first to recognize the mineral as a new species. Montgomeryite occurs in fine striated lamellae ending in pyramids, 5 mm maximum, frequently grouped in subparallel aggregates, in masses or in encrustations of coarse lamellae. The hue is extremely variable, from colorless to dark green, including yellow, red or pale green.

Main photo : Montgomeryite from Tip Top Mine, South Dakota, USA © Jason B. Smith

Montgomeryite from Tip Top Mine, South Dakota, USA © Tom Loomis
Montgomeryite from Elvira Mine, Catalonia, Spain © Christophe Boutry
Montgomeryite from Elvira Mine, Catalonia, Spain © Christophe Boutry
Montgomeryite from Iron Monarch, Iron Knob, Australia © Stephan Wolfsried

Montgomeryite in the World

We encounter montgomeryite associated with other phosphates (crandallite, variscite, triphyllite, etc...) in numerous phosphate pegmatites. The most beautiful samples probably come from the American pegmatites of South Dakota (Tip Top, Etta, etc...), but montgomeryite is also present in the pegmatites of Mangualde and Bandada (Portugal), Lavra da Ilha (Minas Gerais, Brazil) and Sandamap (Namibia). Good specimens have been encountered associated with crandallite in the variscite nodules of Fairfield, Utah, as well as in the Iron Monarch iron phosphate mine near Iron Knob and in the Moculta phosphate quarry (Australia).

Montgomeryite in France

Montgomeryite is not present in the French underground.

Twinning

No twin known for this mineral species.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 4
Density : 2.53
Fracture : Undetermined
Streak : Pale greenish white

TP : Translucent to transparent
RI : 1.572 to 1.582
Birefringence : 0.010
Optical character : Biaxial -
Pleochroism : Low
Fluorescence : None

Solubility : -

Magnetism : NoneRadioactivity : None

ReCaptcha

This service is used to secure web forms of our website and required if you want to contact us. By accepting it you agree to Google's privacy policy: https://policies.google.com/privacy

Google Analytics

Google Analytics is a service used on our website that tracks, reports traffic and measures how users interact with our website content in order for us to improve it and provide better services.

Facebook

Our website allows you to like or share its content on Facebook social network. By activating and using it you agree to Facebook's privacy policy: https://www.facebook.com/policy/cookies/

YouTube

Integrated videos provided by YouTube are used on our website. By accepting to watch them you agree to Google's privacy policy: https://policies.google.com/privacy

Twitter

Integrated tweets and share services of Twitter are used on our website. By accepting and using these you agree to Twitter's privacy policy: https://help.twitter.com/en/rules-and-policies/twitter-cookies

PInterest

Our website allows you to share its content on PInterest social network. By activating and using it you agree to PInterest's privacy policy: https://policy.pinterest.com/en/privacy-policy/