I get a lot of questions about how to read the Diamond suit in relationship readings. This article is an expansion of comments I posted on the Art of Cartomancy Facebook page in answer to some of these questions.
I find that in most cases when Diamonds appear in a relationship reading, they will still talk about money and power and energy. Money and power are often at the root of relationship troubles-- marital problems in particular, so I always take the Diamond cards at face value first, before I consider alternate meanings.
It's important to keep in mind that Diamonds do not represent sentimental feelings. Even the most positive of the Diamond cards cannot assure you that you're going to meet the man of your dreams, or tell you if your crush loves you, or confirm that your lover will return to you.
For the most part the Diamond suit represents energy-- all types of energy including electricity, magnetism, nuclear fission , solar power, light, fire, heat, money (which is energy in motion), consciousness, mental energy, physical energy, sexual energy, and the body's nervous system which controls everything we do.
Diamonds also rule how we perceive energy through our sensory apparatus: eyes, ears, nose, the senses of touch and taste, and of course the extra-sensory abilities such as intuition and psychic awareness. Diamonds represent how we communicate, and how we process information. Diamonds represent information itself.
In general, the Diamonds represent all of the activities associated with left-brain thinking such as analysis, computation, numbers, mathematics, science, logic, speech, language, information technology, computer technology, etc. In other words...
Diamonds are emotionally detached.
Despite this emotional detachment, the Diamond cards play an important role in defining relationships. They show us how we communicate with each other. They can highlight physical and sexual attraction. They can offer clues about the true motives of a prospective partner. They can show us a relationship based solely on financial interests, or one that is based on sex alone. What the Diamonds cannot do is tell us whether or not we will fall in love.
The Ace of Diamonds is a card of communication. It represents a message or an invitation. This Ace can also relate to a new beginning, or to the renewal of an existing situation. In relationship readings, the Ace of Diamonds can also represent a ring. With the right combination of cards from the suit of Hearts, it can represent an engagement ring specifically, and indicate that an engagement is taking place. But unless surrounded by Hearts, this Ace says nothing about love.
Generally, the 2 of Diamonds is a card of self-sufficiency, and the desire for independence. It can define a relationship based on financial interests. It is also the card that represents the imagination. If you are asking about the strong vibes you're picking up from your new office crush, the 2 of Diamonds can warn that it's all in your mind. If you suspect your lover of cheating, the 2 of Diamonds can assure you that you're imagining things.
The 3 of Diamonds talks about stalled growth. It describes relationships that run hot and cold. It can show a lack of commitment in love. One or both parties is unwilling or unable to invest the necessary effort for the relationship to succeed. This card will often show up when the relationship has been on again/off again for a long period of time.
In relationship readings, the 4 of Diamonds represents an energy connection, or good chemistry, which is the foundation for any strong relationship. It is not necessarily sexual, although with love cards the 4 can indeed denote sexual chemistry. This card also shows an intellectual connection. It's a great card for friendship as well.
The 5 of Diamonds is more about sexual attraction, but not necessarily reciprocal. This card reminds us that sex is not love. The 5 is also the energy that surrounds charismatic people and draws others to them. When it falls with a Face Card, the 5 of Diamonds can reveal someone who is attracted to you. Surrounding cards will usually show the nature and degree of the attraction.
The 6 of Diamonds is another card of communication. With spades it shows stubbornness, a lack of communication, withdrawal or holding back. With Hearts it may indicate shyness and timidity. With other Diamonds it usually shows nervousness or an unsettled situation. When it falls in a combination with Hearts and Spades it will highlight feelings of jealousy and possessiveness. The possessive husband or lover will usually show up as the King of Spades with the 6 of Diamonds.
The 7 of Diamonds is a card of earned success. It is about being rewarded for investing time, energy or money. In a love reading, this card can show that a motive other than love is driving romantic interest. It can show what you expect to get out of a relationship. It can show whether or not you are getting what you deserve. With other Diamonds, it can describe a financially convenient arrangement. With Clubs it can be about companionship or the services the partner provides. With Spades it can show co-dependency and the fear of being alone. With Hearts it will indicate investing emotion. The thing to remember is that some kind of a payoff is almost always assumed or expected.
The 8 of Diamonds will describe someone who is guarded and wary. It can represent the need to take things slowly. In relationship readings it can indicate making careful plans for the future. This card is cautious, and lacks any kind of spontaneity.
The 9 of Diamonds is often a person card in relationship readings. It is a card of strong attraction, and will usually represent someone who is attracted to you. This can be your husband/wife or boyfriend/girlfriend, or it can be someone with a secret crush on you. This is also the card of thoughts, and it's an important card to look for if you're asking about what someone thinks of you. Pay close attention to surrounding cards. This person wants something from you.
The 10 of Diamonds can be tricky because it is such a great card. It's big money and security and success and victory. But it is not about sentimental feelings. In relationship readings it can show a union based on financial security. It often shows up as the reason a couple stays together despite serious problems in the relationship.
The Diamond Face Cards can represent people you are attracted to, whereas the Heart Face Cards are people you love. Remember, if you use the suits to describe the Face Cards, they will reflect your (the querent's) perception of them, and not their true state or character. With other Diamonds they are attractive and intelligent and optimistic, restless, nervous and chatty. With Clubs they are helpful, and may offer both advice and financial assistance. With Hearts they can be thoughtful, quiet and shy. With Spades they can be taciturn and stubborn and jealous.
Just because a super positive card appears in a reading, it does not automatically mean that you get your wish. You have to read the card. When in doubt I always ask myself, why did this particular card fall in this position instead of any one of the other 51? There is always a good reason. If you have to fudge or stretch, chances are the cards are not saying what you think (or hope) they are saying.