So you are right that cacao was used as a currency but don't confuse that with how we might use printed fiat currency today.

Their value was relatively small, but they were particularly useful for the markets of the time. They had value because they could be used to make hot chocolate and culturally they were understood to be a useful standard for small value transactions. They were used inside and outside the Aztec Empire.

Sure cacao growing communities had them in ready supply, but mechanisms of taxation and market economies moved cacao beans out of those communities and into wider circulation.

Cacao beans were not the only pseudo-currency, bolts of cotton cloth were used similarly and had a much greater value. The best way to think of either cacao or cotton cloth is as a form of change that could be used to balance transactions. Sure cacao could be used in a pure exchange for something small, but they were just as often used to balance transactions of other items. Say you needed obsidian blades but were selling fine pottery. The value of the blades might exceed that of the pottery so you add a bag of cacao beans to match.

The value and utility of cacao beans lasted for decades after the Spanish conquests. For various reasons colonial Mexico was always cash poor (not enough specie in circulation) which made extensive use of credit and pseudo-currencies like cacao essential for regular commercial transactions. The Spanish even established a formal conversion rate to specie currency. The rate in 1555 was 320 beans to a Spanish silver peso (piece of 8), or 40 cacao beans (a zontle) to a real (1/8 of a peso). By the end of the century it was up to 800 beans to a peso or about 100 to a real. For context, an indigenous day laborer would have made about one real a day. So in other words a small bag of beans 40-100 was about one day's pay for an unskilled laborer.

Here is a Spanish language article on cacao as a currency in both precolumbian and postconquest periods:

Aranda, L. "El uso de cacao como moneda en la época prehispánica y supervivencia en la época colonial." In XIII Congreso Internacional de Numismática, vol. 2, pp. 1439-1450. 2003.

available as a pdf here

Edit: source

I was actually just about to post something sort of similar. I'm not sure it'd be better off as it's own post or mee asking as a follow up question .

Basically, I was curious how the goods and "money" from tribute intersect with the goods/"Money" from Pochteca in terms of the overall economic picture/Aztec (I say Aztec as in the overall hedgemonic empire, since I know tribute was also owed to Tlacopan and Texcoco and was also divvied out to other cities at times as well) economy. Were there any other facets to the Aztec economy besides these two?

Additionally, I was curious about how the logistics of tribute worked. I know the Mexica had a fairly complex, bureaucratic government, so I assume that this was equally complicated and involveed a variety of civil officials. The wiikipedia page lists titles known as Petlacalcatl, Huecalpixque and Calpixque as officials involved with this process.

If I should have this be it''s own post(s), let me know.

One thing to keep in mind when asking this question is that cacao does not grow in the Valley of Mexico. Cacao is a tropical product and highland Mexico does not have the climate to grow the plant. Key areas in Mexico where the crop is (and was) grown are in southern, lowland parts of Mexico like the Gulf and Pacific coasts of the Isthmus of Tehuantepec. So to understand the value of cacao to the Aztecs we first have to understand that, to them, it was an exotic good from the "hot lands."

As such, areas where cacao could be grown were rich areas. The Aztec province of Tochtepec (covering a chunk of the southern part of the modern day state of Veracruz), for instance has a tribute payment of 200 loads of cacao according to the Codex Mendoza. The same tribute demand was made of the far-flung Xoconochco province (the Pacific coast of Chiapas/Guatemala). Both of these provinces also had ancillary benefits beyond their direct tribute, with Tochtepec acting as a gateway to trading in the Maya regions (particularly via the port of Xicalango located roughly on the border of modern day Tabasco and Campeche). Xoconocho tribute of 200 loads of cacao beans were merely a small slice of the cacao trade that Aztecs merchants could then access via trading with local Kiche, Kaqchikel, and other groups, and it is probably not a coincidence that we a see a reference to Aztec visitors showing up in the Annals of the Cakchiquels shortly after the conquest of the Xoconocho region.

So cacao was valuable because it came from far away, and was, by nature, relatively scarce. Cacao is hard to grow, harvest, and process, and even getting a cacao tree to maturity takes years, during which they are not productive, so it is not an easy business to get into. While "the state" was involved in moving cacao harvests to the core Aztec area via tribute, we have a much less well documented concept of opening trade routes which allowed for trading in cacao, both specifically to obtain cacao and as a medium of exchange. I'm not aware of any particular Bill Gates of Cacao among the Aztecs but the pochteca (long distance traders) could certainly become quite wealthy and intermingle with the political elites of the day, although the relationship was more complicated, as I go into here in a response to a follow-up question by /u/jabberwockxeno.