Not an atom of matter enters into the objectivity of commodities as values;
in this it is the direct opposite to the costly sensuous objectivity of commodities
as physical objects. 
                                        –Marx, Capital I

David Harvey doesn’t like Wittgenstein, but Harvey could be paraphrasing Wittgenstein when Harvey interprets Marx as saying “value is immaterial but objective.“ That is, Wittgenstein would argue that, say, a painting’s value isn’t in the painting itself, but rather in the response to the painting, in the language game(s) that determines a painting’s aesthetic qualities and other merits. The relation is immaterial in that one cannot say exactly what it is (per Marx materially, atomically; per early Wittgenstein the nature of the form itself–the nature of, say, a painting’s likeness to what it represents). Money gives this immaterial relation, like any commodity, its objective nature.

If there is a difference between the two, it must be that Wittgenstein is concerned with the commodity’s effect (i.e., pragmatic response or “nonsense” that can only be shown), while Marx is interested in the social process bearing the commodity and the exchange process when “abstract and concrete labor come together.” Yet these processes make value immaterial but objective.

It is interesting to note that some orthodox Marxists believe Harvey here to be suggesting that value isn’t sourced in labor (LTV), which is material. Harvey, however, knows that Marx
does not mean to say that immaterial social relations don’t contain very real, material
bodies. For Marx clearly states, “Now we know the substance of value. It is labour.
We know the measure of its magnitude.
It is labour-time” (Capital I). Value
as a social relation contains both fixed
capital that includes machines and factories and the variable capital of human workers, and these are material in nature. But for Marx value is historical and contextual, too,
a social relation that one cannot get
to or contain in any absolute sense. It is in fact money that gives this immaterial social relation its objective form. Money is the objective representation of value, and value, again, an
immaterial but objective social relation. Money not only measures what is
otherwise unmeasurable and hence gives value its objectivity, but money appropriates
social wealth as individual property (Harvey).

Money “congeals”–conceals–the immaterial social relation, that is, when “exchange processes produce a representation of value in the money commodity, the money form, the universal equivalent” (Harvey). 

There is, however, a difference between material wealth and value:

“And the first thing [Marx] notices [ … ] is that ‘an increase in the amount of material wealth may correspond to a simultaneous fall in the magnitude of its value.’ Value is dependent upon human productivity. Highly productive people can produce a large amount of material wealth
very quickly. And they can work less hours, so actually the amount of value that they make can be very low but the amount of material wealth they generate can be enormous. So again, he’s going to emphasize that distinction between material wealth and value. And he goes on to point out that while changes in productivity affect material wealth, they don’t necessarily have any effect at all on value creation. We will see instances where this is the case, but,
nevertheless, the change in productivity
is itself not directly connected to transformations in value” (Harvey).

Book 1, Ch. 8: Of the Wages of Labour

“[13] We rarely hear, it has been said, of the combinations of masters, though frequently of those of workmen. But whoever imagines, upon this account, that masters rarely combine, is as ignorant of the world as of the subject. Masters are always and everywhere in a sort of tacit, but constant and uniform combination, not to raise the wages of labour above their actual rate. To violate this combination is everywhere a most unpopular action, and a sort of reproach to a master among his neighbours and equals. We seldom, indeed, hear of this combination, because it is the usual, and one may say, the natural state of things, which nobody ever hears of. Masters, too, sometimes enter into particular combinations to sink the wages of labour even below this rate. These are always conducted with the utmost silence and secrecy, till the moment of execution, and when the workmen yield, as they sometimes do, without resistance, though severely felt by them, they are never heard of by other people.”

“[15] A man must always live by his work, and his wages must at least be sufficient to maintain him. They must even upon most occasions be somewhat more; otherwise it would be impossible for him to bring up a family, and the race of such workmen could not last beyond the first generation. Mr. Cantillon seems, upon this account, to suppose that the lowest species of common labourers must everywhere earn at least double their own maintenance, in order that one with another they may be enabled to bring up two children; the labour of the wife, on account of her necessary attendance on the children, being supposed no more than sufficient to provide for herself. But one half the children born, it is computed, die before the age of manhood. The poorest labourers, therefore, according to this account, must, one with another, attempt to rear at least four children, in order that two may have an equal chance of living to that age. But the necessary maintenance of four children, it is supposed, may be nearly equal to that of one man. The labour of an able-bodied slave, the same author adds, is computed to be worth double his maintenance; and that of the meanest labourer, he thinks, cannot be worth less than that of an ablebodied slave. Thus far at least seems certain, that, in order to bring up a family, the labour of the husband and wife together must, even in the lowest species of common labour, be able to earn something more than what is precisely necessary for their own maintenance; but in what proportion, whether in that above mentioned, or in any other, I shall not take upon me to determine.”

“[22] It is not the actual greatness of national wealth, but its continual increase, which occasions a rise in the wages of labour. It is not, accordingly, in the richest countries, but in the most thriving, or in those which are growing rich the fastest, that the wages of labour are highest. England is certainly, in the present times, a much richer country than any part of North America. The wages of labour, however, are much higher in North America than in any part of England. In the province of New York, common labourers earn three shillings and sixpence currency, equal to two shillings sterling, a day; ship carpenters, ten shillings and sixpence currency, with a pint of rum worth sixpence sterling, equal in all to six shillings and sixpence sterling; house carpenters and bricklayers, eight shillings currency, equal to four shillings and sixpence sterling; journeymen tailors, five shillings currency, equal to about two shillings and tenpence sterling. These prices are all above the London price; and wages are said to be as high in the other colonies as in New York. The price of provisions is everywhere in North America much lower than in England. A dearth has never been known there. In the worst seasons they have always had a sufficiency for themselves, though less for exportation. If the money price of labour, therefore, be higher than it is anywhere in the mother country, its real price, the real command of the necessaries and conveniencies of life which it conveys to the labourer must be higher in a still greater proportion.”