Page numbers from Fowkes penguin translation, emphasis is mine

Let us now look at the residue of the products of labour. There is nothing left of them in each case but the same phantom-like objectivity; they are merely congealed quantities of homogeneous human labour, i.e. of human labour-power expended without regard to the form of its expenditure. All these things now tell us is that human labour-power has been expended to produce them, human labour is accumulated in them. *As crystals of this social substance, which is common to them all, they are values - commodity values. *(128)

We have seen that when commodities are in the relation of exchange, their exchange-value manifests itself as something totally independent of their use-value. But if we abstract from their use-value, there remains their value, as it has just been defined. The common factor in the exchange relation, or in the exchange-value of the commodity, is therefore its value. The progress of the investigation will lead us back to exchange-value as the necessary mode of expression, or form of appearance, of value. For the present, however, we must consider the nature of value independently of its form of appearance. (128)

A commodity is a use-value or object of utility, and a 'value'. It appears as the twofold thing it really is as soon as its value possesses its own particular form of manifestation, which is distinct from its natural form. This form of manifestation is exchange-value, and the commodity never has this form when looked at in isolation, but only when it is in a value-relation or an exchange relation with a second commodity of a different kind. Once we know this, our manner of speaking does no harm; it serves, rather, as an abbreviation. (152)

But although price, being the exponent of the magnitude of a commodity's value, is the exponent of its exchange-ratio with money, it does not follow that the exponent of this exchange-ratio is necessarily the exponent of the magnitude of the commodity's value. ... The possibility, therefore, of a quantitative incongruity between price and magnitude of value, i.e. the possibility that the price may diverge from the magnitude of value, is inherent in the price-form itself. *This is not a defect, but, on the contrary, it makes this form the adequate one for a mode of production whose laws can only assert themselves as blindly operating averages between constant irregularities. *(197)

It isn't a duality, it's a series of reflections (commodity-value -> exchange-value -> price). Commodity-value is the socially necessary labour in a commodity, exchange-value is it's reflection in another commodity and price is that exchange value in money. All three of them can differ from each other to some extent (particularly 'commodity-value/value', which can never be actually observed or measured except as seen in its reflection/likeness, exchange-value and the ). All three of these things' ability to diverge from each other is necessary for the capitalist system to function on its laws of averages. Exchange-value is the equivalent of a commodity's commodity-value in another commodity (e.g. the value of a shoe in ounces of gold). Price is a representation of the ratio in which a commodity can be exchanged for money.

Also very important to note (for feminism/ecological/ableism/etc critique) that Marx is laying out the standards of capitalist value, which doesn't necessarily represent the actual work/labour exerted on a given thing, e.g. doesn't represent the labour required to produce a forest cut down.