gems, Ceylon, Sri Lanka, zircon, hyacinth, zirconia, chemical analysis

Guyton de Morveau investigates whether French hyacinth from Espaly and hyacinth from Ceylon are the same mineral, and whether both contain the new earth previously discovered by Klaproth in Ceylon jargon. He compares specific gravity and the effects of heating, finding close agreement between the French and Ceylon material; strong heating removes the reddish color of the French hyacinths, changing them to greenish, nearly white material while retaining or increasing their transparency. He then chemically decomposes the French hyacinth and isolates its constituents. The principal earth exhibits the same distinctive properties that Klaproth had observed in Ceylon jargon and hyacinth. Guyton systematically distinguishes this substance from silica, baryta, lime, magnesia and alumina, concluding that hyacinth contains a new simple earth—what is now known as zirconia—and that the French and Ceylon hyacinths are equivalent in crystallization, specific gravity, hardness, behavior under heat and fundamental chemical composition.