Description

A pair of green tourmaline crystals in matrix, with great lustre, sharp striations and faces. The lower crystal clearly exhibits a phenomenon that is likely present in the upper crystal as well: 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.

These tourmaline crystals appear deeper green at the termination while the remainder of each crystal is a nice mid-green tone.  It seems quite likely to me that the lighter colour is in fact the thinner wall, illuminated from behind by reflection off of the quartz core. These crystals have great contrast with the matrix of lepidolite, feldspar and quartz. The pale lilac crystals of lepidolite are colour-zoned.

The bottom crystal is in pristine condition, and the top crystal is in very good condition from the display angle, incomplete at the back of the termination but this can be displayed out of view – I have photographed it in the third photo from an angle that is to the side/back (not at 90 degrees from the front,  rather about one third of the way around the piece, i.e. at about degree 120 of 360 degrees).  Because they are extracted from enclosing silicate minerals, most Urubu tourmalines are not in such good condition.

A fine cabinet specimen of green tourmaline in matrix, with a great mineralogical phenomenon to go along with it!