According to Eschwege, the total produce of the Brazilian diamond mines for the eighty years, ending in 1823, had not realised the price of one-and-a-half years’ average produce of the sugar and coffee plantations of the same country, although the diamonds cost much more labour, and therefore represented more value.
I definitely overlooked this quote, as "price" had not been discussed much at this point. But that does make sense as a way to understand what he means by "metamorphoses before it can ripen into the price-form".
Your summaries are very helpful!