Pitchblende - Encyclopedia

    Class : Oxides and hydroxides
    Subclass : Oxides
    Crystal system : Cubic
    Chemistry : UO₂
    Rarity : Common

Pitchblende is the collomorphic variety of uraninite. However, although international nomenclature recommends the term uraninite to designate natural tetravalent uranium oxide in all its forms, this term is still often reserved for facies with clear crystalline shapes, the term pitchblende then designating the collomorphic variety of uraninite. Pitchblende is therefore the most widespread variety of uraninite. It forms a series with thorianite and is of hydrothermal origin, common in many veins and uranium-bearing detrital sedimentary rocks. We know that vein pitchblende results from the leaching of uraninite grains disseminated in the granites, the fluids rich in uranium thus formed accumulating in fractures where they precipitate the pitchblende. Very alterable in outcrops, pitchblende epigenizes or transforms into an impressive procession of powdery minerals of yellow to orange hue, rarely black, collectively referred to as "gummites". Its name comes from the German words pech (pitch) in reference to its dull pitch-like luster and blende which is a generic term which designates minerals with a semi-metallic luster, low hardness and high density. Pitchblende is black in color and has a submetallic to resinous luster as well as a conchoidal fracture. It is characterized by a high density (variable depending on the oxidation state of the uranium : from 7.5 to more than 10) and obviously by very significant radioactivity. It commonly constitutes spherulites or aggregates of spherulites whose dimensions can exceed 20 cm in diameter, forming masses with a hilly appearance. It is by far the most important uranium ore.

Main photo : Ptichblende from Pribram, Czech Republic © Eugene & Sharon Cisneros

Uraninite crystals can twin on {111}.

No fakes listed for this mineral species.