Prehnite with Pyrite & Calcite

Prehnite with Pyrite and Calcite from Prospect Quarry, Prospect Hill, New South Wales, Australia, measuring 81 × 71 × 53 mm and weighing 333 grams. The three recorded minerals give this specimen a varied association to explore. It offers more than a single-species example, with a silicate, sulphide and carbonate represented in the supplied identification.

Prehnite is a calcium aluminium silicate containing hydroxyl. Pyrite is iron sulphide, while Calcite is calcium carbonate, so the assemblage brings together minerals with distinctly different compositions. Considering those differences is a useful way to appreciate a specimen as a geological association, rather than concentrating solely on whichever mineral first catches the eye.

Rounded cream-white lobes give the specimen a soft, rolling surface, interrupted by scattered darker points. The outline is broad and irregular, with one more angular projection adding contrast to the rounded forms. An oblique view brings out the relief particularly well, helping the individual lobes stand apart instead of merging into one pale area. The specimen comes from the David Vince Collection. Its interest lies in the combination of a named quarry and three mineral families within one piece. For a collector who enjoys associations, it offers several routes into the subject: the identity of the individual minerals, their differing chemistry and the locality that brings the recorded assemblage together.