Dust, in Ezekiel 26:12, signifies the lowest things which are of the sensual principle of man. They can be either good or bad, depending on the context.

In Isaiah 40:12, the dust signifies exterior or natural truths and goods of heaven and the church.

In Genesis 2:7, the dust is good, and we see some interesting nuances:

First, there's this: 'To form the man, dust from the ground' is to form his external man, which had not previously been man... (Arcana Coelestia 94)

Here, this formation of our external body and mind is a precursor, setting the stage for God to "breathe into our nostrils".

In Arcana Coelestia 1610, we find this passage, where again, dust has a good signification:

'Dust of the earth' has regard to those things that are celestial, for, as shown already, 'the earth' means the celestial aspect of love; 'dust of the sea' has regard to those things that are spiritual, for 'the sea', as has also been shown, means the spiritual aspect of love; while 'as the stars of heaven' means both but in a higher degree. And because these things cannot be numbered they therefore became common expressions to describe growth and multiplication beyond measure.

Then, in Arcana Coelestia 3707, these ideas get pulled together:

The reason the dust of the earth symbolizes goodness is that the earth, [or land,] symbolizes the Lord’s kingdom and therefore goodness, as shown just above in §3705. The dust of that land, then, means goodness, but earthly goodness, since the land symbolizes what is lowest in the Lord’s kingdom....

But there are bad connotations, too. In Micah 7:14-17, licking dust symbolizes being only sensual - bodily and external, worldly, and selfish. It's much the same in Psalms 72:9, where "Barbarians will bow down before God, and His enemies lick the dust...". See Arcana Coelestia 249, 3413 for interesting explanations of this.

(Odkazy: Apocalypse Explained 1145)

3707. 'And your seed will be as the dust of the earth' means that Divine natural Truth would be as natural good. This is clear from the meaning of 'seed' as truth, dealt with immediately above in 3706, 'your seed' - that is, Jacob's - consequently meaning Divine natural Truth, for as shown above 'Jacob' represents the Lord's Divine Natural; and from the meaning of 'the dust of the earth' as good, dealt with in 1610. Consequently 'your seed will be as the dust of the earth' means in the internal sense that Divine natural Truth will be as Divine natural Good. The reason 'the dust of the earths means good is that 'the earth' means the Lord's kingdom and accordingly good, as shown just above in 3705. 'The dust of the earth' therefore means good, though natural good since the earth, as also shown in that place, means that which is lower in the Lord's kingdom, thus the natural, while heaven when mentioned as well means that which is interior, or the rational. This is why the fruitfulness of good and the multiplication of truth are described in various places by means of expressions stating that someone's seed will be as the stars of heaven and as the dust of the earth. 'The stars of heaven' in that case means rational concepts, and 'the dust of the earth' natural images, which will increase in this fashion. What is meant by natural truth becoming as natural good will in the Lord's Divine mercy be explained later on.