FACET
A facet is one of the flat surfaces of a cut stone or glass.

FACETING
Faceting is the cutting and polishing of the surface of a stone.

FANCY DIAMOND
Fancy diamonds are rare diamonds that are red, blue, green, or purple; these diamonds are quite valuable. Diamonds are precious, lustrous gemstones made of highly-compressed carbon; they are one of the hardest materials known. Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419.

FANCY CUT
Fancy cut stones are cut in unusual ways. Some fancy cuts include the heart, fan, rivoli, trapezium, cathedral window, half-moon (lunette), kite, and triangle.

FANTASY CUT
The fantasy cut is a new way of faceting stones that uses freeform angles - virtually anything goes.

FAUX
Faux means false. A faux gem is an imitation.

FEATHER
A feather is an internal flaw (also called an inclusion) in a gemstone that can start at the surface of the stone and extend deep inside. Feathers can either ruin a stone (by making it fragile and/or changing the color), or add to its beauty.

FELDSPAR
Feldspars are a family of minerals that include moonstone (adularia), amazonite, sunstone, and labradorite.

FETISH
A fetish is a charm, amulet, pendant or other decoration associated with magical properties; it often represents an animal or person.

FIBULA
A fibula is a brooch (pin) that looks a bit like a safety pin. Fibulas have been used since ancient times to secure clothing.

FIGURAL
Figural jewelry is disigned to look like real objects. Common subjects are the human body, animals (especially butterflies, dogs, cat, birds, and shells), flowers, leaves, and everyday objects (like baskets and fans).

FILIGREE
Filigree is gold or silver wire that have been twisted into patterns and soldered into place. Openwork filigree is not soldered onto a sheet of metal and is difficult to make. Imitation filigree is made of stamped metal.

FINDINGS
Findings are the parts that jewelers use in making jewelry. For example, clasps, hooks, pin backs, jump rings, and earring backs are findings.

FINENESS
Fineness is the proportion of silver or gold in a metal alloy. Fineness is usually expressed in parts per thousand. For example, the fineness of sterling silver is 925.

FINGER RING SIZE
To size a finger for a ring, a finger-ring gauge is used. The rings are marked with their size and the person determines which one fits well. Another, less accurate method is a cardboard card with cut-out holes marked with the ring sizes. To determine the ring size of a finger using the circumference of the finger, or to determine the size of a ring given its diameter.

FIRE
A stone's fire is the streaks of brilliant color within it. Good quality opals have a lot of fire.

FIRE OPAL
Fire opals are a type of opal that is firey orange to red in color (but have no opalescence). These opals are rarely transparent - they are usually milky. Opal is a mineral composed of silica (and some water) and is a species of quartz. Many opals have a high water content - they can dry out and crack if they are not cared for well (opals should be stored in damp cotton wool). Opals have a hardness of 5.5 to 6.5 and a specific gravity of 1.98-2.50. Fire opals are found in Western Australia, Mexico, Brazil, Guatemals, and Honduras.

FIRESTONE
Firestone is an imitation iridescent rainbow quartz. It is made by heating rock crystal until it crazes; it is then put into dye as it cools.

FLAW
A flaw is a an imperfection in a gemstone. Flaws include: cracks, inclusions of other minerals or liquid-filled cavities. A flawless stone is called "clean." Flaws can greatly reduce the value of a stone, but in some cases, like moss agate or rutilated quartz, the "flaws" increase the value of the stone.

FLOATER NECKLACE
An floater (or invisible) necklace looks as though the beads are simply floating on the skin; the beads or pearls are strung far apart from one another on an almost invisible string (like clear fishing line).

FLORENTINE FINISH
A Florentine finish on a metal's surface reduces the metal's reflectivity. It is accomplished by engraving parallel lines into the surface using a sharp tool, and then making more lines or curves at right angles (cross-hatching).

FLUORESCENCE
Fluorescence is property in which light (or other radiation) is emitted from an object. Many stones (including some diamonds) flouresce when exposed to ultraviolet light.

FOB
A fob is a short chain or ribbon that attaches to a pocketwatch; it frequently had a decorative medallion or other ornament attached to one end. Fobs were worn hanging from a pocket. Fob is also the word for the small pocket in trousers that held a pocket watch. The word fob is also commonly used for the fob charm itself.

FOILBACK
A foilback (or foiled stone) is a stone that has a metallic foil backing; this thin metallic backing is frequently composed of mercury and tin. Silver-colored, gold-colored, or other-colored foil is applied to the back of a stone to make the stone more reflective. Before scintillating cuts (like the brilliant cut) were invented, even precious stones were foiled to enhance their sparkle. Moisture can damage foil and make the stone "dead," losing its brilliance. Stones are rarely foiled any more.