Facet - a flat surface polished onto a gemstone. An example would be a round brilliant cut diamond which has either fifty-seven or fifty-eight facets.
Fancy Cut (Shape) - any gemstone shape other than round.
Filigree - a type of decoration on metal ware made by use of fine wire, plain, twisted or plated. It is used to form delicate and intricate designs.
Finish - the polish and overall symmetry of a faceted gemstone.
Fire - the flashes of spectral colors of the rainbow usually found in colorless or near colorless gemstones such as diamonds. When the gemstone is tipped and rocked under bright light the colors will seem to move around the gemstone. Fire can also be found in some colored gemstones.
Flaw - any visible imperfection found within a gemstone. (Note: this is one term that I find is over used and abused within the jewelry industry. This term is usually used when describing internal characteristics of gemstones that we refer to as inclusions. All gemstones have inclusions with the exception of "flawless" gemstones. In reality all gemstones are "flawed". All gemstones that are removed from the earth have them. It is the cutter that removes the inclusions when they want to produce a "flawless" gemstone. They are what I like to refer to as the gemstone's finger prints. They are actually a good thing to have. For example, when identifying diamonds they help a Gemologist separate two diamonds that may look alike.)
Florentine - a cross hatch pattern of closely set engraved lines forming a decorative surface or finish on a piece of jewelry.