Facets
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Flat surfaces on a cut stone or glass.
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Fancy Diamond
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Rare diamond of intense colour.
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Feldspar
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A large group of minerals that is found in a wide area of the earth, but only a few of its members, including moonstone, is suitable for gemstones.
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Filigree
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A gold or silver wire that has 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.
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Flaw
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An imperfection in a gemstone. A flawless stone is called a “clean”.
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Fresh water pearls
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Pearls cultivated in molluscs, not oysters, found in fresh warm lakes and rivers. They are generally elongated in shape and have a milky translucent appearance. Their wide range of interesting shapes make up in fashion appeal for their relatively low value.
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Fluorite
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Fluorite is a mineral that comes in many colours, including purple, red, pink, yellow, green, blue, black, and multi-coloured stones. Crystals are transparent to translucent. Fluorite is in many parts of the world.
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Fly-back date hand
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In a chronograph with analogue display, an additional centre second hand which can remain superposed on the other one as it moves, can be stopped independently and then made to "fly back" so as to catch up with the other hand, can be stopped and reset to zero together with the other hand. An example is a hand which indicates the date against a scale and then flies back to the beginning of the month after reaching the 28th, 29th 30th or 31st day, according to the month and leap year.
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Frequency
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Defined by the number of oscillations per second. In quartz watches, the frequency is generally 32,768 oscillations per second. It is commonly expressed by the abbreviation Hz (Hertz).
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