Strong’s Greek
G4556 — sardios
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
σάρδιον
sardios — pronounced sar'-dee-os
properly, an adjective from an uncertain base; sardian (3037 being implied), i.e. (as noun) the gem so called:--sardius.
1 occurrence in the KJV.
Revelation 21:20
The fifth, sardonyx; the sixth, sardius; the seventh, chrysolyte; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst.