ROMÉ DE L'ISLE (J.-B. Louis de). Essai de cristallographie, ou description des figures géométriques, Propres à différents corps du règne minéral, connus vulgairement sous le nom de cristaux. Paris, Didot, 1772; in-8 (189 x 127 mm), fawn calf, spine ribbed and decorated, fillets on the boards, inside indent (Binding of the period). 10 plates; 2 large folding tables. ORIGINAL EDITION of the founding work of crystallography. It was during his travels in India and China that Romé became interested in natural history and precious stones. The chapter on gem crystals studies the shape and colour of different varieties of diamonds, sapphires, rubies, etc., and how to counterfeit them by heating Brazilian topaz. This essay was the prelude to the Law of Constancy of Angles, which he set out in 1783. A very fine copy. The first leaf, blank, has not been preserved.