The 4 C's:
Cut - Refers to the number, placement and shape of the facets that create a finished diamond. A stone's cut will determine it's quality and sparkle-ability.
Color - Diamonds come in a wide variety of colors but most common is the clear, colorless, white diamond. Color grades are as follows: D-F Colorless (white); G-J Nearly colorless; K-M Faintly yellow; N-R Very light yellow; S-Z Light yellow; Z+ "Fancy" colors.
Clarity - Determined by how free of imperfections (on the outside and inside) the stone is. Clarity grades are as follows: F1=flawless; IF=internally flawless; VVS1/VVS2=very, very slightly imperfect on the inside; VS1/VS2=very slightly imperfect on the inside; SI1/SI2=slightly imperfect on the inside; I1/I2/I3=imperfect.
Carat - a unit of weight. One carat equals 200 milligrams or 100 points.
Brilliant - round and the most popular throughout history.
Princess - square cut, more contemporary in style.
Emerald - rectangular in shape.
Radiant - similar to emerald with the underside cut with more facets.
Marquise - Pointed at the top and bottom with rounded sides.
Oval - elongated round shape.
Pear - round at the bottom and pointed on top, like the shape of a pear.
Heart - very romantic notion, but the least sparkly.
Settings: Bezel - metal rim that fully surrounds the stone. Half Bezel - metal rim that surrounds the stone on either side but not top or bottom. Tension - a compression-spring pressure holds the stone in place between the band. Prong - three to six "claws" that hold the stone in place. This is the most commonly used. Channel - numerous stones sandwiched between two channels of metal, but no metal between them. Bar - thin vertical bars of metal between the stones secures them in place. Pave - three or more rows of small stones secured by raised metal. Gypsy - this setting sets the stone "flush" into a hole in the metal.