Calciet - Optische calciet "IJslands spat" (China)

The double refraction on this thing is wild — set it over a line of text and you get two crisp copies instead of one. Clarity is way better than I expected for a natural specimen, barely any internal veining to muddle the image.

Held this piece up to a printed page and the text doubled clear as day, which is exactly what I was hoping for from optical calcite. There's one small internal fracture near the edge, but it doesn't interfere with the double refraction at all.

Turned my phone screen into a tiny rainbow when I tilted this thing just right, and the double refraction is way sharper than the cheap calcite I had before. The piece arrived with clean edges and no cloudy patches, which matters a lot for optical grade. Been sitting on my desk as a fidget ever sinc