Man has been fascinated by gems since ancient times, though none can say with certainty when he first discovered them. For thousands of years, gems were worn as charms or amulets to protect people from demons and diseases. Even today many people wear gems as their birth stones.

All gems are called 'precious sones'. But more specifically, the word 'precious' is used for the four most valuable stones - the diamond, the ruby, the emerald and the sapphire. The other valuable stones are called semiprecious stones, and these include opals, ametysts and topazes.. In ancient times gems were distinguished only by their colours. All precious stones with a red hue were called 'rubies', all green stones were called  'emeralds' and all blue ones 'sapphires'. Now a days well-established scientific tests have been developed to identify different gems. What are these gems and how are they found?

A precious stone is a mineral that occurs naturally in the rocks of the earth. Diamonds are obtained from the Igneous rocks. Sedimentary rocks are the source of turquoise and opal. Metamorphic rocks are a source of rubies. The word 'gem' comes from the Latin word 'gamma' which means 'bud'. As a bud blossoms into a lovely flower, dull lumps of a mineral can be cut and polished into brilliant shapes.

But not all gems are obtained from minerals. For example, the pearl is a gem that is not a stone. It is obtained from a sea creature called oyster. Amber is formed from the resin of trees which existed millions of years ago. Corals are produced by tiny sea animals. Diamonds are composed of only one element, i.e., pure carbon. The mineral corundum is the source of rubies and sapphires. Rubies get their red colour because of small quantities of chromium oxide present in aluminium oxide. Certain other gems, such as topaz, tourmaline, garnets and jade are members of the silicate group. Some gems belong to the quartz group, which is pure silica ( silicon dioxide), but contain 5 to 10 percent water.

Now scientists have also developed methods to manufacture many of the gems synthetically. Synthetic gems are made of the same materials which natural gems contain. For instance, rubies and sapphires are made by melting aluminium oxide in an induction furnace and adding some impurities for colour.