Boyd’s Bible Dictionary:
A variously hued gem, corresponding to the modern chrysolite, which the Hebrews obtained from Ethiopia
(Job 28:19), and which constituted the second stone in first row of the high priest’s breastplate (Ex. 28:17), and a foundation stone of the New Jerusalem (Rev. 21:20).
Concise Bible Dictionary:
The Hebrew word is pitdah, and has been supposed to be derived from an island in the Red Sea called Topazos. This would account for the ancient versions calling it “topaz,” but the gem is supposed to agree with our chrysolite. Job 28:19 speaks of “the topaz of Ethiopia.” It was one of the jewels in the breastplate (Ex. 28:17; Ex. 39:10); and is included in the prophetical description of the symbolical “king of Tyrus” (Ezek. 28:13). In the New Testament τοπάζιον, points to the same stone (Rev. 21:20). It is a silicate of magnesia and iron, and being comparatively soft has to be worn with care.
Strong’s Dictionary of Greek Words:
Transliteration:
topazion
Meaning:
neuter of a presumed derivative (alternately) of τόπαζος (a "topaz"; of uncertain origin); a gem, probably the chrysolite