In cartomancy with playing cards, the Jack of Diamonds (J♦) is the card of the messenger.

Like the other Jacks, the Jack of Diamonds can, albeit rarely, indicate an actual person, usually a kid or teen. This kid is smart and energetic, mostly positive. More likely, however, the card is one of communication. It is the archetype of the mercurial bearer of news, and it is neutral. If followed by negative cards, it shows bad news. With cards of blockage, it shows delays in receiving news.
The Jack of Diamonds is also the card of the go-between, not unlike the corresponding Vera Sibilla card. It indicates someone or an agency mediating between two parties. Sometimes it indicates the process of mediation itself.
Finally, the Jack of Diamonds can signify the knowledge of facts and acquiring knowledge of facts as an extended meaning of the idea of message. As such, this is one of the playing cards connected with study and studying.
In love readings, the card often signifies messages, but it can also show the presence of a third party mediating between two lovers, although this was more common in the past. This is especially when the Jack falls next to a face card.
In career readings, the Jack of Diamonds indicates much the same. If it describes a job, it indicates one that requires a certain level of education. It can also be a job dealing with information. Needless to say, it shows students.
Psychologically, the card shows a lively intellect and much nervous energy. Usually a person influenced by this card will find it hard to keep his mind still and often looks for new stimuli. Spiritually it indicates signs and messages from above (or from below, with the appropriate cards, as, unlike the Jack of Hearts, that of Diamonds is too mercurial to be inherently good)
Combination:
J♦ + 2♦ = it can be a literal postman bringing correspondence | a student
6♦ + 9♣ + J♦ = worry about a delay in the arrival of a message or package
J♦ + Face + 4♥ = an agreement reached thanks to a third person
J♦ + 6♠ = in addition to indicating messages about sickness, it indicates mediation efforts gone awry
2♣ + J♦ = it can indicate studying (intellectual steps)








