Specimen with two trigonal quartz crystals.

Crystal 1 : photo 1. Quartz (m, r, z, -pi). Great faces -pi that make faces r and z nearly to disappear.

Crystal 2 : photos 2, 3 and 4. Quartz (m, r, -pi, +pi, and c ?). Here, face z has disappeared, and we have great obtuses faces -pi and +pi, +pi most rare than -pi. Furthermore, an undefined flat face similar to the pinacoïd (face c 00.1, an extremely rare face for the quartz), is visible.

These quartz crystal are showing a crystallographic rarity that become in the Orpierre area in France : new faces on the hexagonal pyramid of some rare quartz. It is an obtuse rhombohedra, called -pi (01-12). It can come sometimes with its opposite rhombohedra, called +pi (or pi) (10-12). Moreover, a more obtuse rhombohedra can appear (extremely rare), the rhombohedra -omega (01-13) and its opposite, omega (10-13). The study of these quartz have been done by Roger Martin, a suisse scientist, and published in the suisse magazine "Le cristallier Suisse" in  1973, 1974, ...
I extracted the pictures of his studies and join then in the last photos.