"This publication is the catalogue of the Diamonds exhibition, 8 July 2005-26 February 2006, originally created by the Natural History Museum, London, under the administration of Dr. Michael Dixon" -- p.2.
OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
Diamonds : the world's most dazzling exhibition by Natural History Museum. ISBN 0565092014. Published by Natural History Museum in 2005. Publication and catalogue information, links to buy online and reader comments.
