In Exodus 28:19, it is not certain what kind of stone this was, but it was azure from white, which signifies spiritual good. It also signifies natural good, or that of the lowest heaven. (Arcana Coelestia 9870, True Christian Religion 609)

An agate, one of the precious stones in Aaron's breastplate, signifies the spiritual love of good (Exodus 28:19).

9868. 'A chrysoprase, a sapphire, and a diamond' means the celestial love of truth, from which the things that follow spring. This is clear from the meaning of these stones as the celestial love of truth, dealt with below. The reason for saying 'from which the things that follow spring' is that all the forms of good and truths that follow emanate in order from those that go before; for the existence of anything unconnected with others prior to itself is not possible. First in order is the celestial love of good; second is the celestial love of truth; third is the spiritual love of good; and fourth is the spiritual love of truth. This order is what was represented in the rows of stones in the breastplate of judgement, and it is the actual order of the forms of good and the truths in the heavens. In the inmost heaven there is the celestial love of good and the celestial love of truth, the celestial love of good constituting the internal part of that heaven, and the celestial love of truth the external part of it. But in the second heaven there is the spiritual love of good, which constitutes the internal part of it, and the spiritual love of truth, which constitutes the external part of it. Each love furthermore flows into the next in the same order, and they constitute a unified whole so to speak. From this it is evident what should be understood by 'from which the things that follow spring'.

[2] As regards the stones belonging to this row, they derive their meaning, as the previous ones and also all the others do, from their colours. For the meaning of precious stones is determined by their colours, see above in 9865; colours in heaven are modifications of the light and shade there, and so are diverse forms of intelligence and wisdom among angels, 3993, 4530, 4677, 4742, 4922, 9466, the light in heaven being Divine Truth emanating from the Lord, the source of all intelligence and wisdom. Being of different shades of red the stones belonging to the first row mean the celestial love of good; but the stones belonging to the present row are of different shades of blue that is the product of red. For there is blue which is the product of red and blue which is the product of white. Blue which is the product of red shines inwardly from a source that is flaming; this is the kind of blue by which the celestial love of truth is meant. But blue which is the product of white, such as is present in the stones belonging to the next row, which means the spiritual love of good, does not shine inwardly from a source that is flaming but from one that is clear and bright.

[3] Whether chrysoprase, the first stone belonging to this row, was of a blue colour cannot be proved from the derivation of that word in the original language. But the fact that it means the celestial love of truth is evident in Ezekiel,

Syria was your merchant because of the multitude of your handiworks; [they exchanged for your wares] chrysoprase, purple, and embroidered work. Ezekiel 27:16.

This refers to Tyre, by which wisdom and intelligence arising from cognitions or knowledge of goodness and truth are meant, 1201. Chrysoprase is linked here with purple, and since 'purple' means the celestial love of good, 9467, it follows that 'chrysoprase' means the celestial love of truth; for wherever good is spoken of in the prophetical part of the Word, truth belonging to the same class is also spoken of, on account of the heavenly marriage in every detail there, 9263, 9314. 'Syria' too, which was 'the merchant', means cognitions of good, 1232, 1234, 3249, 4112, the cognitions of good being the truths of celestial love.

[4] A sapphire, the second stone belonging to this row, is - as is well known - of a blue colour, like that of the sky; therefore it says in the Book of Exodus,

Seventy of the elders saw the God of Israel, and under His feet there was so to speak a work of sapphire, and it was like the substance of the sky for clearness. Exodus 24:10.

This stone means what is translucent with inner truths, which are the truths of celestial love, see 9407.

[5] But a diamond, the third stone belonging to this row, means the truth of celestial love, on account of its translucence that tends to have a blueness in it. Thus it is through this stone, being the last, that the colours of the stones belonging to this row and also the previous one shine, and are then brought in contact with those in the next row. The situation is similar with the goodness and truths in the inmost heaven and the goodness and truths in the heavens that come after it. The latter goodness and truths derive their life of charity and faith from the former by transmission, as if by a shining through.