A prized specimen of pyrite in a cubic crystal form, my collection. I was lucky to buy this from a Middle Eastern dealer at the Tucson Rock and Gem show this year, and for a low price near the end of the show. This large pyrite crystal measures 7/8" long and seems perfectly formed. The matrix is limestone and you can see a tiny bit of another pyrite crystal at the back of the specimen near the center top. That one measures 3/8"
Getting this photo was quite a trick. I put it on a cardboard box and shot it in early morning light outdoors. I was wearing a green t-shirt and that gives the slight green glow on the face of the crystal towards the front view. I had to be careful how I positioned myself for the crystal is so smooth and perfect it reflects everything. On the face of the crystal to the right in this image, you can see how it reflects the limestone at far right. For a few other views of neat specimens of pyrite, see these two images of pyrite (museum quality) that I don't own but was lucky enough to find and photograph:
Calcite crystals with pyrite on the bevels:
Pyrite discs (dollars):