Malachite
These are malachite crystals- the specimen is about 1.5" wide. Malachite is a copper carbonate, and usually forms very fine grained sprays of crystals (see next photo). I shot this in sunlight against a black sheet of paper with a macro lens.
John Christensen
NIKON CORPORATION NIKON D7000, f/18 @ 60 mm, 1/320, ISO 250, No Flash
© John N Christensen