Jacinth (/ˈdʒæsɪnθ/, /ˈdʒeɪsɪnθ/) or hyacinth (/ˈhaɪ.əsɪnθ/) is a yellow-red to red-brown variety of zircon used as a gemstone.
In Exodus 28:19, one of the precious stones set into the hoshen (the breastplate worn by the High Priest of Israel) is called, in Hebrew, leshem, which has often been translated into English as "jacinth". The modern identification of leshem with jacinth seems to have been popularized by Martin Luther.
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Zircon (/ˈzɜːrkɒn, -kən/) is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is ZrSiO4. An empirical formula showing some of the range of substitution in zircon is (Zr1–y, REEy)(SiO4)1–x(OH)4x–y. Zircon precipitates from silicate melts and has relatively high concentrations of high field strength incompatible elements. For example, hafnium is almost always present in quantities ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal system. The natural color of zircon varies between colorless, yellow-golden, red, brown, blue, and green.
The name derives from the Persian zargun, meaning "gold-hued". This word is changed into "jargoon", a term applied to light-colored zircons. The English word "zircon" is derived from Zirkon, which is the German adaptation of this word. Yellow, orange, and red zircon is also known as "hyacinth", from the flower hyacinthus, whose name is of Ancient Greek origin.