Category Gems and Stones


Diamond mines produce both gem-quality and industrial diamonds. Although most of the diamonds sold are industrial diamonds, the value of the gem diamond trade is much greater. Africa is the richest continent for diamond mining, accounting for around 49 per cent of world production. Artificial diamonds are made for use in industry. Most artificial diamonds are made in the United States.

A total of only 314 tonnes of diamond has ever been mined in the whole history of diamond mining. The world’s total of all gems, industrial, natural and synthetic is around 57 tonnes per year.

The world’s famous diamonds

The Star of Africa is the world’s largest cut diamond. It was cut from the biggest diamond ever found and is included in the British Crown Jewels. The Smithsonian pink diamond, although small, is extremely valuable because of its unusual colour.

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Weighing gemstones

Diamonds and other gemstones are weighed in a special unit. This is called a ‘carat’. There are five carats (cts) in one gramme. Therefore 1 kg is 5,000 cts. Tiny diamonds have their own measure. They are weighed in ‘points’. One carat is 100 points, so a quarter-carat gem (0.25 ct) is a ‘twenty-five pointer’. Gold is also measure in carats but these are not based on weight. They are amounts of gold in metal, and 24 carats is equivalent to 100 per cent pure gold.

Testing for hardness

By comparing other stones with the hardness of a diamond, a test called the ‘hardness test’ was developed. Minerals can be tested by measuring their hardness. In the diagram, the hardness value of several different substances is given. This is called the Mohs scale and measures hardness from one, representing talc, to ten — diamond — with the highest hardness value.

Calcite is a colourless mineral found in limestone; gypsum is a white mineral and is used for making plaster.

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Gemstones play an important part in our lives. We use gems in medicine, space travel, weather forecasting, and engineering in industry. Without them we would not be able to drill into the Earth’s crust to extract oil, which has numerous uses in today’s world. However, the extraction of gemstones can cause a number of environmental problems.


During the mining process, large areas of vegetation are cleared to allow for the exploration of the area, the actual mining and the processing of the gemstones retrieved from the mine. As a result, the animals and plants in the area are wiped out.


The heavy digging and lifting machines used in the mining industry pump out carbon monoxide, hydrogen and oxides of nitrogen and sulphur. These can be harmful to humans and wildlife. The carbon monoxide is converted into carbon dioxide in the atmosphere. This contributes to the greenhouse effect — global warming — which could devastate our planet if it is not controlled.


Usually, a lump of rock bigger than a house must be crushed and sorted to find one small gem. This waste must be disposed of safely so that it does not cause further damage to wildlife. The crushing of waste rock also produces a lot of dust, which can hang in the air, making breathing uncomfortable. Water drainage from mining processes carries acidic waste products into rivers, causing harm to the local ecosystem.


Many gems are rare. Even gems that are thought of as common, such as amethyst, are rare compared to most rocks in the Earth’s crust. To conserve these rare stones, scientists have found ways of creating artificial gemstones, mainly for use in industry.

The future

To protect the environment from damage caused by gemstone mining, it must be managed properly. This means that governments and mining companies must stick to rules that encourage waste to be disposed of safely. They must also limit destruction of ecologically important areas, such as habitats that contain endangered species of plant or animal life.

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Gems have played an important part in medicine since around the 1960s. Rubies are used to produce a laser beam in certain types of lasers. Ruby lasers are used in the removal of skin blemishes, such as tattoos. However, there can be side-effects to this treatment, such as scarring and a removal of natural skin colour in the area.

Diamond has many special properties. Hard diamond chips are used on dental drills to allow them to cut easily through teeth. Many kinds of radiation can travel easily through diamond and it can withstand huge pressures. This makes it suitable for use in space, and in weather and spy satellites. Perfect diamonds are used on space probes, as they are unlikely to be damaged by the deadly gases found on some planets, such as Venus.

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Quartz is often used in precision instruments. Scientists discovered that when quartz crystals are put in an electric field, they will vibrate. The precise way in which the quartz is cut affects the speed at which it vibrates. This exact vibration is used as the beat to keep time in a ‘quartz’ clock or watch. Tiny ‘jewel’ bearings, often rubies, are fitted inside clockwork watches. They are used because their surfaces are not worn away by the workings of the watch.

High-quality natural diamonds are used to make fine scalpel blades for surgeons to use in delicate eye operations. The precision-made stylus in a record player pick-up is also a diamond and therefore lasts for a long time. Heat flows through diamond very easily, so tiny diamond pieces are used in television transmitters to keep electronic devices cool.

A quartz watch

In a quartz watch, a battery produces electric pulses. These electric pulses ‘wobble’ the quartz. As long as the battery continues to do this, the quartz will ‘wobble’ at an exact rate to create a steady pulse. This helps to keep the watch showing the correct time.

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Diamond is harder than any other substance. It can cut through anything. For this reason it has many uses in industry. Diamond powder is used for polishing lenses and gems, and for sawing tiny silicon wafers to make computer chips. Diamond is used in drills to make holes in stone and concrete. Whole ‘stones’ are used for engraving glass, as teeth in large saws for slicing stone and as drills powerful enough to cut holes in road surfaces. They are also set into the drills of oil and gas wells exploring under the sea bed.

In the future, diamonds may be used to make very small and powerful computers, radiation detectors, unwettable and unscratchable surfaces and as light emitters in electronic displays.

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Some types of gems are made as imitations of more valuable gemstones. Often, cheaper natural gems that look similar are used. For example, citrine looks like the more costly topaz. Sometimes, artificial gems are used.

‘Gemologists’ test gems and crystals to find out exactly what they are made of. They have to look closely inside the gem through a lens or a microscope. They also test the quality of light coming out of a gem and can tell whether the sapphire is artificial or natural.

Gemstones can be sandwiched together with other substances to create ‘gems’ that can be sold for more than they are really worth. This method is also used to create cheaper jewellery.

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We have seen how crystals are made up of atoms fitted together in regular patterns. These patterns can be made to change — with dramatic results! Black graphite is made of carbon atoms; diamond is also made up of carbon atoms but arranged in a different pattern. By applying huge amounts of pressure the carbon atoms in black graphite can be squeezed together to make a more compact diamond pattern. This process is only used to make industrial quality diamonds. It’s too expensive to make a diamond large enough to be set into a ring.

A hard, sparkling, artificial substance called cubic zirconia (CZ) is made into gems which look just like diamond. CZ gems are much cheaper than diamonds.

Ruby and sapphire furnace

Artificial crystals are made in furnaces. Rows of these furnaces make clear, sausage-shaped crystal rods of ruby or sapphire. These are cut in great numbers to make very inexpensive gems. Other kinds of furnaces are used to make perfect crystals which are used in lasers. CZ crystals are made in special furnaces at temperatures of more than 2,500°C.

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There are many ways of shaping, or ‘cutting’, a gemstone. A person who cuts gems is called a ‘lapidary’. The gems are cut to display their colour, fire, sheen or other beautiful optical effect. Gems are sliced with diamond saws and ground into flat facets or curved surfaces. They are then polished with diamond or ruby powder.

Many clear gems are cut with flat, mirror-like facets. Their angles are carefully set to allow for the way that the light ‘bends’ as it enters and leaves the gem. Each kind of gem has its own special set of facet angles: brilliant cut ruby has different angles from topaz, for example. A faceted gem will twinkle or show its colour well only if it has been cut with correct facet angles.

Different types of cut: (a) emerald, (b) pear, (c) round, (d) oval, (e) marquise.

‘Cabochons’ are gems that have been cut in the shape of a dome. This type of cut shows off bright colours in opaque gems — gems that do not let light through. Cabochons are also made to reveal beautiful tricks of light, such as ‘stars’ in certain rubies and sapphires, the sheen in moonstones, colours in opals and the bright line which can be seen inside the rare, honey-coloured ‘cat’s eye’ gems.

The ‘emerald cut’ is oblong with the corners cut off. Long facets reflect lots of light back from deeply coloured, transparent gems. Some gems are carved so that little scenes, symbols or figure-heads stand out. These are called ‘cameos’. Opals are often cut into cabochons to show off their colours.

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A diamond can be cut and shaped only by another diamond. This is because diamond is the hardest substance known to man. Each diamond crystal can only be cut in certain directions, along which it is a little less hard. Even so, it takes hours to saw through a diamond. Diamonds can also be split, or ‘cleaved’, along four different directions through the crystal.

Nearly all diamonds are ‘brilliant cut’. This means that the facets — faces of gems — are cut at just the correct angles to make the most of a diamond’s sparkle. Each facet acts like a polished mirror inside the gem — it reflects the light and splits it into the colours of the rainbow.

There are several different stages involved in shaping a diamond crystal into a cut gem. Firstly, the crystals are sent to special factories and sawed with thin bronze discs coated in diamond dust and olive oil. The designer decides where each crystal is to be sawed.

Each diamond is then ‘bruted, or shaped. The bruter shapes the gem by holding another diamond against it while it is spun around at great speed. After grinding and smoothing the top facet, or ‘table’, the cutter carefully decides where to grind the first of the 16 main facets.

When the main facets are polished to the right size, the ‘brillianteer’ grinds the other 40 small facets. Over half of the original crystal has now been cut or ground away!

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