Wulfenite, (w. Mottramite and Calcite)

Chemistry: PbMoO4
Size: 137 x 135 x 105 mm
Owner: Liam Schofield
Photographer: Olga Kaspera

This specimen is of paragenetic interest because it features two generations of wulfenite, the first of which occurs as very large crystals.  The display surfaces (Photographs 1 and 2) feature tabular, canary-yellow crystals of wulfenite (to 10 mm) distributed rather sparsely over a matrix comprising dark-green mottramite that has been extensively encrusted by white, rhombohedral calcite.  The underside of the specimen (Photograph 3; FOV c. 80 mm) reveals that the mottramite "matrix" has, in fact, overgrown an earlier generation of very large platy crystals of tan-coloured wulfenite, the largest of which measures at least 95 mm across.  This accounts for the unusual undulating surface of the mottramite / calcite matrix (Photograph 4; FOV c. 50 mm).    

The paragenetic sequence, therefore, appears to be:  wulfenite (I) >> mottramite >> calcite >> wulfenite (II)