Acceptability
    Durability
    Divisibility
    Stability
    Portability
    (Elasticity)

If it spoils or decays within your lifetime it's not a currency.

If it's not something you can divide in order to make payments of a more-or-less arbitrary amount, it's not a currency.

If you can't predict how much of the asset you will need to pay your bills next month, it's not a currency

If you can't bring it with you to the place where the exchange takes place, it's not a currency.

If you can't obtain capital investment in a currency because the currency itself is more valuable than anything you could produce, then it's not a (good long term) currency. This last one is in parens because it one only matters in a growing economy. A deflationary currency can still otherwise function as a viable medium of exchange, but eventually, lack of availability for new entrants will mean that entrepreneurs will begin looking to do business in alternate currencies.

Though I do personally think there's a lot more to a currency than that.

1. Dividend payments

2. The expectation that someone else will want the stock more in the future. (Often for reason #1.)

Financially, there is no other logical reason to possess stocks. It was part of the larger lesson that companies often perform irrational actions because they are made primarily out of people.

BC has none of those advantages.

https://en.m.wikipedia.org/wiki/European_Currency_Unit