What is a pegmatite in geology ?

Pegmatite : definition

A pegmatite is an igneous rock of granitic composition occurring in the form of veins or clusters occupying the periphery or the immediate proximity of granitoid massifs, characterized by the large size of its minerals (several centimeters to several meters). Pegmatite crystals hold most of the mineral world's size records : the largest known crystals of microcline, biotite, muscovite, spodumene, beryl, etc... have been extracted from them.

The term pegmatite is however incomplete and must be accompanied by a qualifier : granitic pegmatite, syenitic pegmatite, etc...

Pegmatites form between 370°C and 600°C and represent the end of crystallization of granitic magmas. Their essential minerals are those of granite : quartzfeldspars and micas, to which are frequently added rare minerals, called pneumatolytic (beryl, lepidolite, topaz, cassiterite, rare earth phosphates, tourmaline, etc...) resulting from the concentration in the last fluids of volatile and incompatible chemical elements (B, Be, Li, Zr, Nb, Ta, La, Ce...).

The particular pegmatites, devoid of quartz and associated with nepheline syenites and ultrabasites are called "pegmatoids".

Orthoclase and topaz from Pakistani pegmatites
Aquamarine and muscovite from Pakistani pegmatites
Tourmaline from Pakistani pegmatites

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/