Each month of the year has its own gemstone, which becomes the birthstone for those born in the month. The origin of birthstones is believed to date back over 3000 years to the time of the High Priest Aaron who wore a sacred breastplate decorated with twelve gemstones. These became associated with the twelve months of the year.
Garnet - January
Garnet crystal (4 cm) in schist rock, Austria, and two garnet gemstones. Read more
Amethyst - February
Amethyst crystal group (12 cm) Brazil, and amethyst gemstone. Read more
Aquamarine - March
Aquamarine crystal (6 cm) and two aquamarine gemstones. Read more
Diamond - April
A diamond crystal in rock (4 cm), Udachnaya Mine, Siberia and a diamond ring and an un-mounted diamond. Read more
Emerald - May
Emerald crystal group (6 cm) Siberia and emerald ring. Read more
Pearl - June
Blister pearl in the shell of a freshwater oyster (14 cm) and a pair of pearls. Read more
Ruby - July
Ruby crystals in rock (6 cm) from Mysore, India. Below left below, three synthetic rubies and right one real ruby gemstone. Read more
Peridot - August
Peridot crystal (1.5 cm) from St. John's Island in the Red Sea, and two cut peridot gemstones. Read more
Sapphire - September
Clockwise from top left: blue ‘star’ sapphire (2 cm), yellow sapphire crystal, Ratnapura, Sri Lanka, synthetic yellow sapphire gemstone, blue sapphire gemstone Sri Lanka and blue ‘star’ sapphire gemstone. Read more
Opal - October
Top: a vein of opal in rock (6 cm), New South Wales, Australia, Opal tie-pin Lanyon Collection, pale opal, Australia, 4.70 carats in ‘marquise’ cut, dark opal, Australia, 7.55 carats in ‘heart’ cut. Read more
Topaz - November
Blue topaz crystal (6 cm), Ural Mountains, colourless topaz gemstone, topaz gemstone Read more
Turquoise - December
Turquoise veins in rock (5 cm) and two turquoise gemstones. Read more
January - birthstone is garnet
Garnet is a mineral that forms in conditions of high pressure, so it typically occurs in metamorphic rocks.
Most garnets in the jewellery trade are dark red, but garnets also occur in shades of green and orange.
The weight of gemstones is measured in carats; five carats make one gram.
The garnet gemstone (left) from Mozambique weighs 15.31 carats and the slightly bigger stone of unknown provenance weighs 19.25 carats.
Confusingly, the same word ‘carat’ is also used in jewellery when describing gold and silver. However, in the case of the precious metals, ‘carat’ measures their purity, not their weight.
February birthstone is amethyst
This amethyst crystal group is from the Julius Hanna Collection of minerals which was bought by the Belfast Art Gallery and Museum (now Ulster Museum) for £50 in 1926.
Mr Hanna was a director in the Belfast engineering firm Musgrave & Co. Ltd, which manufactured stoves, exporting them world-wide. He and his wife lived in grand houses in the suburbs of east Belfast.
The amethyst gemstone, 61.01 carats weight was bought in 1996 for £2824.00 (£31.00 per carat).
Amethyst is the purple variety of quartz. Other gem varieties of quartz are Rock Crystal (clear), Citrine (yellow), and Cairngorm (dark brown).
March birthstone is aquamarine
Aquamarine is the blue variety of beryl, a beryllium and aluminium silicate.
The crystal is from an old collection of minerals which was in the possession of the Earls of Caledon, County Armagh and later the Royal School, Armagh.
The smaller stone (left) weighing 3.51 carats is a rare Mourne Mountains aquamarine stone. It was cut by the London jewellers Max Davis in the 1970s from a crystal supplied by the Ulster Museum. Very few Mourne aquamarine gemstones exist.
The larger stone (right) is an aquamarine from Brazil, 21.73 carats. It was bought from London dealers in 1996 for £2824.00 (£130.00 per carat).
April birthstone is diamond
Diamond which is the crystalline form of carbon is the hardest naturally-occurring material. The formation of diamond occurs at great depth. Subsequent earth movements bring the diamond bearing-rock close to the Earth’s surface, where it can be mined.
The Udachnaya Diamond Mine which was opened in 1955 is the third deepest open-pit diamond mine in the world.
The ‘gent’s signet ring’ is a diamond of a 1.75 carat weight set in gold of 18 carat purity. The stone is colourless and is termed a ‘brilliant’. This ring was bought for £2,100 in 1987.
The un-mounted stone is yellow-tinged and these diamonds are sometimes called ‘Cape’ diamonds. This diamond was bought for £2,034.00 in 1989.
The two diamond gemstones have been faceted in the ‘round’ cut, which best shows the brilliance of diamonds.
May birthstone is emerald
Emerald is the green variety of the mineral beryl, which is aluminium and beryllium silicate. Other gem varieties of beryl are aquamarine (blue) and morganite (pink).
There are many styles of cut for gemstones. Often it is the gemstone which determines the cut. For, example, emerald with its elongated crystal shape is best suited to a rectangular cut. In time this rectangular cut came to be called 'emerald' cut. There is a bewildering array of names given to the many different styles of cut.
The stone weighing 16.45 carats is set in an 18 carat gold shank with diamond-set shoulders. This stone is from Colombia, which produces the world’s finest emeralds.
June birthstone is pearl
A pearl is a natural gem created by a living organism.
When a piece of grit gets inside an oyster the animal coats the irritant with a substance called ‘nacre’. Layers of nacre, also known as ‘mother of pearl' build up around the grit to form a pearl.
Nacre is composed of slender calcite crystals arrayed in one direction, so that light falling on nacre is vividly reflected. This causes the pearl to produce the wonderful radiance when seen in light.
This fresh-water oyster (a bivalve mollusc) was taken from the Clady River, Gweedore, County Donegal in 1986 by a pearl fisherman. When he opened it, he discovered a ‘blister-pearl’, seen on the left of the shell.
Pearls used in jewellery are not naturally-occurring. They are ‘cultured pearls’ grown in pearl farms in the warm seas of the tropics. The grit is skilfully placed into the oysters and the nacre then grows around this irritant in optimum conditions to form high-quality pearls.
This pair of Japanese pearls was bought for £112 in 1996. They are a variety of pearl known as ‘Mabe’. These pearls have flattened bases, caused by the special positioning of the irritant in the oyster shell. This makes Mabe pearls more suitable for mounting in brooches, rather than being used in the more traditional pearl necklace.
July birthstone is ruby
The Ulster Museum bought this ruby sample from mineral dealer Richard Barstow in 1979 for £9.00.
Barstow (1947-1982) who began work in the Cornish mining industry became a passionate mineral collector while still a teenager. He made his hobby his livelihood in 1972 when he set up in business as a mineral dealer. He was gifted at describing his mineral samples in concise and informative sentences and his mineral lists form a valuable data-base of minerals and their localities.
By 1980 Barstow had become the U.K.’s foremost mineral dealer and ‘Barstow specimens’ feature in the geology collections of many museums. Sadly, Richard Barstow died of cancer at the young age of 35 in 1982.
Ruby is the red variety of the mineral corundum which has a simple chemical make-up, aluminium oxide. This makes it easy to synthesise ruby in the laboratory.
Synthetic stones are a legitimate gem variety in the jewellery trade, so long as they are not passed off as natural gemstones.
The real ruby gemstone is a 2.65 carat ruby from Thailand, bought from Hatton Gardens jewellers Raymond Taghioff for £13,250 in 1989. Good quality rubies fetch a high price.
August birthstone is peridot
Olivine which is a magnesium-iron silicate, is an inconspicuous dark mineral found in igneous rocks. However occasionally it forms large green crystals of gem-quality making them suitable for use in jewellery. This gem-quality olivine is known as peridot.
St John’s Island also known as Zeberget is a fragment of deep crustal rock that has been thrust up and exposed on the surface. This rock contains the world’s finest peridot crystals and they have been mined on the island for 3500 years.
This crystal was bought from London mineral dealers for £60.00 in 1979.
The peridot gem (left) which is a St John’s Island stone weighs 13.02 carats. It was bought from the London jewellers Raymond Taghioff in 1989 for cost £1562.00.
The periodot gem (right) was cut from a peridot pebble already in the museum’s collection. The pebble was panned from the gravels of a river in Arizona, U.S.A.
September birthstone is sapphire
It comes as a surprise to newcomers to gemmology to learn that both sapphire and ruby are varieties of the mineral corundum. It is a further surprise to find out that sapphire, as well as being blue also occur in hues of pink, orange, yellow, green, purple, black and even colourless.
Some sapphires, when cut in the rounded cabochon style reflect light in six-rayed patterns. This is caused by the internal arrangement of the stone. Such stones are termed ‘star sapphires’.
As with ruby, synthetic sapphires can be synthesized in the laboratory.
The star sapphire crystal was bought at Sotheby’s auction 9th July 1968; yellow sapphire crystal cost £125.00 in 1979; yellow synthetic sapphire was one of a number of synthetic stones bought in 1985; blue sapphire (6.37 carats) from Sri Lanka was bought for £1,670 in 1989; and the cabochon star sapphire (4.72 carats) is of unknown provenance.
October birthstone is opal
The legend that opal brings misfortune is based on the fact that opal breaks easily.
This is because opal, although it has the chemical formula - silicon dioxide – of the hard mineral quartz, does not have the crystal structure of quartz. Instead, in opal the atom groupings of silicon and oxygen occur in a non-crystalline arrangement. This means opal tends to break if dropped. This led the superstitious to believe that opal is unlucky.
However, this non-crystalline positioning of the atom groups in opal makes light rays passing through it interfere with each other, producing rainbow-like iridescence. This results in the mineral showing vivid hues of blue, green and red, making opal an irresistible gemstone.
Australia accounts for 97% of the world’s production of opal and it is the national stone of the country.
These three opal gemstones are on display in ‘Earth’s Treasures’, the Ulster Museum’s permanent mineral display.
November birthstone is topaz
In antiquity the name topaz was loosely applied to yellow and brown gemstones. In fact, topaz which is a fluorine-rich silicate occurs as colourless, yellow, red-brown, light blue, pinky-red and pale green crystals.
The blue topaz crystal is from the Mursinka locality in the Ural Mountains, Julius Hanna Collection. Below are: colourless topaz gemstone, 33.90 carats, bought for £318.00 in 1992; and a sherry coloured topaz gemstone, 16.50 carats, bought for £6,300 in 1992 - topaz gemstones of this colour are sometimes styled ‘Imperial topaz’.
There is a bewildering terminology in the jewellery trade to describe the styles of cut and colours of gemstones.
Colourless crystals of topaz have been collected from granite in the Mourne Mountains.
December birthstone is turquoise
The name ‘turquoise’ means ‘Turkish stone’ because the trade route that brought it to Europe was through Turkey.
Turquoise is mostly found in arid regions where it occurs as encrustations and veins in rock. Chemically turquoise is copper-aluminium phosphate with some iron, but the composition is variable.
The beautiful blue colour of turquoise attracted attention from earliest times and turquoise was used for decoration in Egypt in the times of the Pharaohs.
The rock sample with the turquoise vein (5 cms) is from the mineral-rich Karkaralinsk area of Semipalatinsk Province, Siberia.
The turquoise gemstones are: left cabochon cut stone 6.75 carats weight, from Iran; and right a darker cabochon cut stone 10.00 carats from Arizona, USA.