Zircon is another word for jacinth.
Rev.9:17 And thus I saw the horses in the vision, and them that sat on them, having breastplates of fire, and of jacinth, and brimstone: and the heads of the horses [were] as the heads of lions; and out of their mouths issued fire and smoke and brimstone (sulphur).
A short video showing Zircon
Zircon (/ˈzɜːrkɒn, -kən/)[7][8][9] is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium.
Jacinth /ˈdʒæsɪnθ/[1] or hyacinth /ˈhaɪəsɪnθ/[2] is a yellow-red to red-brown variety of zircon used as a gemstone.[3]
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 is often translated into English as "jacinth".[4] The true identity of this stone has been a source of confusion since at least the first century; the modern identification of leshem with jacinth seems to have been popularised by Martin Luther, who may in turn have been following a fourth-century tradition.[5]
In Revelation 21:20, one of the foundation stones of the New Jerusalem is hyacinth (Greek: hyakinthos).[6] However, Strong's Concordance and Thayer's Greek Lexicon describe this as a stone of the colour of the hyacinth plant, i.e. dark blue.[7] The stone intended may be the sapphire.[8] In Revelation 9:17, the word appears in adjective form (hyakinthinous, "hyacinthine");[9] this, again, is thought to be descriptive of a blue or purple colour, with no reference to the modern jacinth stone.[10]
King of king's Bible
Exodus 28:19 And the third row a ligure, an agate, and an amethyst.
King of king's Bible
Revelation 21:20 The fifth, sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst. (see the Breast-Plate of Aaron - Exodus 28)