In the book of Exodus, God had the Jacinth stone placed first in the third row of the Breastplate of Judgement. In the book of Revelation, Jacinth is the eleventh foundation stone in the Heavenly Jerusalem. 
In his 7th Century Commentary on the Apocalypse, St. Bede the Venerable, writes:

"Jacynth changes with the face of the sky. For when this is serene, it is clear and pleasing; but when it is cloudy, it pales and becomes dull before the eyes. And it indicates souls which are always given up to heavenly contemplation, and which, in a certain way, and so far as is permitted to mortals, approach the angelical life." 

​[Ref.: Ex. 39:12 , Rev. 21:20; St. Bede the Venerable, Commentary on the Apocalypse]
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