SOME ROUGH CRYSTALS are beautifully shaped and has breathtaking lustre and colour, but most are worn down or have other surface imperfections. A skilled stone cutter and polisher, called a lapidary, can turn these stones into objects of beauty and value by using their individual qualities in the right way. Beads and cabochons are the oldest cuts for such materials as lapis lazuli and turquoise, and carnelian and agate. Brilliant-cut diamonds are known from the 17th century and this is the most popular cut today.
Cutting a brilliant
A lapidary first studies a rough stone with a powerful lens called a loupe. This shows the direction of grain and the flaws. The stone is marked to show where it should be sawn and the facets are then ground.
QUESTIONS AND ANSWERS on Crystal and Gems
Ques. How long have people been mining for gemstones?
Ans. jewellery has been found in burial sites dating back thousands of years. Ancient jewellery is rare, but some Ancient Egyptian pieces have survived. These are often made of gold set with gems such as turquoise, lapis lazuli and carnelian.
Ques. What are potato stones?
Ans. Potato stone is a name given to a geode, a hollow ball of rock encrusted inside with amethyst or other crystals. The crystals form when silica-rich liquids seep into gas bubbles in volcanic lava and magma as they cool. Also known as thunder eggs, geodes are highly prized.
Ques. Why are gemstones so precious?
Ans. Gemstones are valuable because of their natural beauty, their durability, their rarity, and the way in which they are cut and polished. There are 3,000 different kinds of mineral, but only about 100 could be classed as gemstones, making them very rare.
Ques. Where do diamonds come from?
Ans. Diamond forms at extremely high temperatures and pressure 80 km (50 miles) or more below the ground in the Earth's mantle. When diamonds were first discovered, 2,000 years ago, they were mainly found in river gravel. These days, most diamond is mined from kimberlitic rock. Australia is the main producer today, but diamonds are also mined in Africa, the former USSR, Brazil and the USA.
Ques. What are seed pearls?
Ans. Pearls vary in size, the smallest of all being seed pearls. Pearls are not weighed in carats like other gemstones, but in grains. One grain = 0.05 g (0.002 oz). Seed pearls weigh less than 0.25 of a grain.
Ques. Why were children often given coral jewellery in the past?
Ans. Coral was thought to protect the person wearing it from evil. For this reason, children were often given coral necklaces end bracelets to keep them healthy and safe from harm.
Ques. Why are emeralds green?
Ans. The characteristic green colour of ..emeralds come from tiny amounts of cromium and vanadium.
Ques. Why are gemstones cut and polished?
Ans. Cutting and polishing gemstones transforms them into jewels. It maximizes the amount of light they reflect so that they sparkle and shine.
Ques. Why organic gems are often carved rather than cut into facets?
Ans. Organic gems, such as coral, ivory, amber, jet and pearl are softer than mineral gems and are often opaque. For this reason, they are often carved and polished. Light cannot shine through them, so it is pointless cutting them into facets to increase their brilliance.
Ques. What is the connection between rubies and emery boards?
Ans. Rubies are one of the most expensive gems. Ruby is a variety of the mineral corundum, which is second in hardness to diamond. Emery is an impure form of corundum and has been used as an abrasive for thousands of years.
Ques. Which famous ruby isn't really a ruby at all?
Ans. Many crown jewels around the world contain massive red gemstones called spinels that people mistook for rubies. The huge Black Prince's Ruby in the British Imperial State Crown is in fact a spinel, given to the Black Prince in 1367 by the King of Spain as a token of his appreciation.
Writer –Dr.R.F. SYMES and Dr.R.R. HARDING