gems, Ceylon, Sri Lanka, zircon, hyacinth, jargon

Haüy compares the stones then called hyacinthe and jargon de Ceylan to determine whether they are actually the same mineral. Building on Klaproth’s chemical analyses, which had revealed a high proportion of the newly recognized “zirconian earth” in both, he examines four mineralogical characters: specific gravity, hardness, double refraction and crystal structure. He finds their physical properties closely comparable and demonstrates particularly strong double refraction in both. Crystallographic analysis shows that their apparently different crystal habits can be derived from the same primitive structure. Haüy therefore unites hyacinth and Ceylon jargon under the name zircon, describing several zircon crystal forms and recording a number of them from Ceylon, including material occurring in a river descending from the island’s central highlands. The paper is an important early step in establishing differently colored “hyacinth” and “jargon” as varieties of a single mineral species rather than distinct gemstones.