A fine green tourmaline crystal in matrix, with a deeper green zone at the termination while the rest is an attractive mid-green. Nice contrast with the matrix of lepidolite, feldspar and quartz. In very good condition, a small chip along the prism edge and some contacting at the termination edge. Because they are extracted from enclosing silicate minerals, most Urubu tourmalines are not in such good condition.
Tourmalines from the Urubu Mine often exhibit a fascinating phenomenon: the core of the elbaite has been hollowed out and replaced by quartz. This has been discussed by John S. White in “Quartz Cores in Tourmaline Crystals” (Rocks & Minerals, 90:5, September/October 2015, 462). It is believed that the original cores of these tourmaline crystals were pink elbaite, more susceptible to dissolution in certain circumstances, and so the crystals became hollowed green shells, subsequently filled by quartz. I suspect that the lower (lighter zoned) section of this crystal has a quartz core. A partial tourmaline crystal on the back of the specimen shows a cross-section with a quartz core (last photo).
A very nice aesthetic green tourmaline cabinet specimen!