Diamonds may be a girl's best friend, but the job for the photographer is to make them irresistible to every woman. Let's look at two different ideas for the commercial representation of the diamond.
Some people think that additional backgrounds are good for this gem because it can depict beautiful people who are happy to have the ring, bracelet, or whatever jewelry item it is that is presented. This kind of photo might be good on the cover of a magazine, but on a page with several other products, it doesn't work that well.
Even with plenty of printable space to gucci display a large picture, most retailers will agree that you keep the attention on the subject of what you are selling. The item that is the focal point of the shoot is usually rather small in relation to the size of a person, and panoramic views tend to detract from the very thing you want everyone to see.
Obviously, the other train of thought is for the diamond to be represented in its natural beauty. It is what the potential buyer wants to see, and the greater it can be made to look in size, the better it will hold the attention of the viewer.
By taking something small and making it appear large, you have not tried to misrepresent the product. You have only clarified the image to make it easier to see the detail and beauty of the diamond, but the subconscious mind of the person who is interested in the jewelry might well envision it larger than it is.