Krohnkite is an uncommon hydrated sodium copper sulfate, and good crystals ONLY came from the type locality of Chuquicamata, Chile. This was a great mine, totally unique in its chemistry, that once produced an amazing suite of specimens. Krohnkite is particularly beautiful. It is lustrous and translucent and exhibits the most beautiful color. Normally krohnkite is more a pure blue but this crystal shows blue with addition of emerald green hues. A significant, old example of a great species. This has an old Ward's Science label with it (circa mid-1900s, I would guess) .