Copper-bearing (Paraíba-type) Tourmaline

from a cover included in the Roskin Gems Report

Copper-bearing (Paraíba-type) tourmaline is highly valued in the gem trade, particularly those from Brazil. Distinguishing stones from Brazil, Mozambique and Nigeria can be challenging, and an article on pp. 772–787 describes the use of machine learning to geochemically separate material from these three localities.

The stones on the cover are rescaled to similar visual size, and from the upper left, they consist of a 9.3 ct oval from Mozambique, a 5.2 ct cushion from Brazil, a 19.3 ct pear shape from Mozambique, a 60 ct cushion from Nigeria and a ring containing a 4.3 ct oval from Brazil.

The matrix specimen of Cu-bearing tourmaline, feldspar and quartz is approximately 8 cm wide and is from Brazil.

Images by Luc Phan, SSEF; digitally arranged by Dr Michael S. Krzemnicki. The ring is courtesy of Wilds Company Ltd (Hong Kong).