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A mollusc whose shell is iridescent on the inside. Abalone is a source of mother of pearl which is used in jewellery making. Also known for its delicious edible flesh.
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Akoya pearls
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One of the most familiar types of cultured pearls, grown in pearl oysters off the coast of Japan. They are known for their orient and warm colour and rarely grow to more than 9mm in size.
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Alexandrite
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A mineral (a type of chrysoberyl) that appears in different colours depending on whether it is viewed in natural or artificial light. It appears to be red when seen in candle light and blue to green when seen in fluorescent light. Alexandrite was discovered on the birthday of the Russian Czar Alexander II and was named in his honour. It is mined in Russia, Brazil, Burma, Ceylon, and Rhodesia.
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Alloy
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A combination of two or more metals. Common alloys used in jewellery include gold with less than 24 carat (mixed with silver, copper, and/or other metals), sterling silver (92.5% silver, 7.5% copper), brass (roughly half copper and half zinc), bronze (at least 60% copper with tin and possibly other metals), and pewter (tin, lead, antimony, and a little silver or copper).
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Amber
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A translucent fossilised resin (from conifers) that comes in a range of colours including, yellows, reds, whites, blacks and blues. When rubbed, amber produces static electricity. The best quality amber is clear.
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Amethyst
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A relatively common form of mineral quartz. It is usually purple but can vary in colour from pale lavender to a deep, reddish purple. Deeper-coloured amethysts are more highly valued but synthetic ones are hard to differentiate from the real stone.
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Amplitude
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Maximum angle by which a balance in a watch swings from its position of rest.
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Analogue display
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Indicates the passing of time by a marker (usually in the form of hands) on a scale on the watch dial.
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Annual calendar
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A watch showing the day, date, month and 24 hours, adjusting automatically for short and long months. The calendar needs setting only once a year - from the end of February to the 1st of March.
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Aperture
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Small opening in a watch. The dials of some watches (in French: montres à guichet) have apertures in which certain indications are given (e.g. the date, the hour, etc).
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Aquamarine
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A transparent light blue or sea-green stone. Today, blue aquamarines are more highly valued, but this was not always the case. Large aquamarines are relatively common and the best ones come from Brazil.
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Arm-in-the-air watch
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A scene or figure on a watch dial with parts that move to indicate the time in hours and minutes when a button is pressed.
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Astronomical watch
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A timepiece with any indication of time depending on the sun, moon or stars, such as equation of time, moon phase, sidereal time, sun hand, time of sunrise and sunset, zodiacs, and star disc.
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Automatic watch
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A watch whose mainspring is wound by the movements of the wearer's arm. On the basis of the principle of terrestrial attraction, a rotor turns and transmits its energy to the spring by means of an appropriate mechanism. This means the watch does not have to be recharged manually and, unlike a quartz movement, does not need a battery. The system was invented in Switzerland by Abraham-Louis Perrelet in the 18th century.
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Azurite
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A mineral that is normally opaque and azure-blue. It is misleadingly called “blue malachite” to distinguish it from “green malachite”. It is sometimes used in jewellery in flat-top pieces.
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