Strong’s Greek
G5191 — huakinthinos
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
ὑακίνθινος
huakinthinos — pronounced hoo-ak-in'-thee-nos
from 5192; "hyacinthine" or "jacinthine", i.e. deep blue:--jacinth. see GREEK for 5192
1 occurrence in the KJV.
Revelation 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.