This Matter of Birthstones - Compendum Caidis
'The earliest mention of gemstones being definitely associated with the months of the year is in the “Antiquities of the Jews” by Flavius Josephus writing in the first century, A.D. To quote:
“Moreoever, the vestments of the high-priest being made of linen signifies the earth, the blue denotes the sky, being like lightning in its pomegranates, and resembling thunder in the noise of the bells. And as for the ephod, it showed that God had made the universe of four elements, and as for the gold interwoven in it, I suppose it related to the splendor by which all things are to be enlightened. He also appointed the breastplate to be placed in the middle of the ephod to resemble the earth, for that occupies the middle place of the world; and the girdle, which encompassed the high priest about, signifies the ocean, for that goes about everything. And the two sardonyxes that were in the clasps on the high-priest’s shoulders, indicate to us the sun and the moon. And for the twelve stones, whether we understand by them the months, or the twelve signs of what the Greeks call the zodiac, we shall not be mistaken in their meaning.”'
Jerusalem