Isaiah 54:12 - Matthew Poole's English Annotations on the Holy Bible

Agates; one kind of which stones was transparent like glass, as Pliny writes in his Natural History, b. 37. ch. 10. But some render this word crystal, and the LXX., and some other of the ancients, translate it jasper. But the proper signification of the Hebrew names of precious stones is unknown to the Jews themselves, as hath been noted before. It may suffice us to know that this was some very clear, and transparent, and precious stone. Thy borders; the utmost parts or walls. The church is here evidently compared to a building, whose foundation, pavement, gates, and windows were named before.