A diamond solitaire refers to any piece of single-diamond jewelry, though it often refers to engagement rings. Round shapes are popular for solitaires, though many cuts and colors are appropriate for such jewelry, according to About.com Jewelry expert Carly Wickell.
When buying solitaires, three qualities should be evaluated in addition to overall size, or carat weight. These include the stone's color, clarity and cut. Though the color depends on the type of stone selected, a white stone should be nearly colorless. Next, the diamond should be clear and free of clouding imperfections. Finally, the stone's cut should have good proportions and uniformity, both of which affect brilliance.