Strong's Greek #4556 - σάρδιον, ου, τό sardion (sard)

sardius.

Properly, an adjective from an uncertain base; sardian (lithos being implied), i.e. (as noun) the gem so called -- sardius.

Strong's 4556: σάρδιον

σάρδιον, σαρδίου, τό (neuter of σάρδιος, see below), sard, sardius, a precious stone, of which there are two kinds, concerning which Theophrastus, de lapid. 16, 5, § 30, Schneid. edition says, τοῦ γάρ σαρδίου τό μέν διαφανες ἐρυθροτερον δέ καλεῖται θῆλυ, τό δέ διαφανες μέν μελαντερον δέ καίi ἄρσεν, the former of which is called carnelian (because flesh-colored; Hebrew אֹדֶם, the Sept. σάρδιον, Exodus 28:17; Exodus 36:17 (Exodus 39:10); Ezekiel 28:13; ἁιματοεντα σαρδια, the Orphica, de lapid. 16, 5), the latter sard: Revelation 4:3 (Rec. σαρδίνῳ); Revelation 21:20 G L T Tr WH. Hence, the adjective σάρδιος, σαρδια, σάρδιον (from Σάρδεις, cf. Pliny, h. n. 37, 7) sardine namely, λίθος (the full phrase occurs Exodus 35:8 (variant)): Revelation 21:20 Rec. (B. D., see under the words, Sardine, Sardius.)

Strong's Greek: 4556. σάρδιος (sardion) — 2 Occurrences

Revelation 4:3 - N-DNS
GRK: ἰάσπιδι καὶ σαρδίῳ καὶ ἶρις
NAS: stone and a sardius in appearance;
INT: jasper and a sardius and a rainbow

Revelation 21:20 - N-NNS
GRK: ὁ ἕκτος σάρδιον ὁ ἕβδομος
NAS: the sixth, sardius; the seventh,
KJV: the sixth, sardius; the seventh,
INT: the sixth sardius the seventh