Sphalerite (and gersdorffite). Nenthead, North Pennines, Britain
This is the same field of view as 58d but in transmitted light. The fine scale of the growth banding in sphalerite is very clear. In thin section or polished thin section, much of the fine detail would be lost. The intensity of the colours are due to variations in the trace element content of the growth bands, most importantly the iron content.
Doubly polished thin section, plane polarized light, x 40, air