The prominent dioptase crystal here is not only doubly-terminated, but is nearly a full inch in length and is super lustrous and transparent to translucent! The big Dioptase emanates tremendous internal reflections that enhances its deep emerald green color and the luster is off the charts! The subordinate crystals, mostly on the right side, and a few tiny ones on the left, have the same wonderful characteristics. There is just a touch of Calcite matrix on the back of the piece as a finishing touch, and some contact in the back so it is not quite 360 degrees but is otherwise perfect. Superb - I could not imagine a better dioptase thumbnail for the combination of qualities here!