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)

249. 'Eating dust all the days of its life' means that the sensory part had become such as could live from nothing else than the bodily and the earthly, and so had become hellish. This too is clear from the meaning of 'dust' in the Word, as in Micah, 7:14, 16-17.

Shepherd Your people as in the days of eternity. The nations will see and be ashamed at all their might, they will lick the dust like serpents of the earth they will be shifted from their strongholds.

'Days of eternity' stands for the Most Ancient Church, 'nations' for people who put their trust in the proprium, who are referred to as 'licking dust like a serpent'. In David,

Barbarians will bow down before God, and His enemies lick the dust. Psalms 72:9.

'Barbarians' and 'enemies' stand for those who look solely to earthly and worldly things. In Isaiah,

Serpents, dust will be their bread. Isaiah 65:25.

Because 'dust' meant people who did not look to spiritual and celestial things but to bodily and earthly, the Lord commanded the disciples to shake the dust off their feet if a city or house was not worthy, Matthew 10:14. For more on 'dust' meaning that which is condemned and hellish, see at verse 19.