In Hindu astrology, the nine planets of the solar system are represented by precious stones. The navaratna as they are called, became extremely popular even amongst Mughal invaders. It was popularly believed that wearing suitable stones brings in luck and good fortune. Though several gems are used in Indian jewels, only nine of them are termed as Navaratna. They are the Ruby, Pearl, Diamond, Coral, Emerald, Topaz, Sapphire, Gomedha and Cat's Eye. Out of these Ruby, Pearl, Diamond, Emerald and Sapphire are qualified as Maharatnas meaning the Most Superior Gems.

According to Hindu mythology there are three kinds of gems - those that belong to swarga loka (heaven), to patala loka (hell) and to mrityu loka (valley of the dead).

The four gems that belong to swarga loka are:

Chintamani is white in colour and is worn by Brahma

Kaustubhamani the colour of a lotus flower is worn by Vishnu

Rudramani is gold in colour and is worn by Shiva

Syamantakamani is a brilliant blue gem worn by Indra.

The serpents that inhabit patala loka wear precious gems in black, blue, yellow, green, white, red, pink and milky colors. All precious and semi-precious stones known on earth are stones of the mrityu loka.

Stones that are rare and durable are called as gem stones. "A precious stone is a small, rare, hard stone which has inherited from nature the name beautiful." Significant characteristics of any gem stone are rarity, hardness, natural origin and beauty together with chemical resistance.

While Diamond, Ruby, Emerald and Sapphire are termed as precious stones, Opal, Jade, Amethyst, Aquamarine and Garnet are called semi-precious stones. These semi-precious stones are sufficiently attractive to be used in jewellery, but are not so rare and hence termed as semi-precious stones.

Precious stones:

Diamond is one of the precious stones that appears to be colourless when viewed with a naked eye, but has different shades. Colour variations occur from the extreme temperature and pressure degree, dating back to millions of years, when diamond was created.

Fancy coloured diamonds like vivid green, blue (like world’s famous diamond - HOPE), pink and red diamonds are some of the rare and valuable pieces. A single colour grade can significantly affect a diamonds value. Yellowish tinges are found due to traces of nitrogen making it very rare. Main countries where diamonds can be found are South Africa, Australia and Russia.

Ruby is one of the precious stones. The presence of a small amount of chromium oxide is responsible for its rich hue. Apart from colours the value of a ruby depends on clarity. This stone has less number of inclusions. The top quality ruby is of red colour. The word ruby is a Latin word for red - Ruber that is derived from similar words in Persia, Hebrew and even Sanskrit. "The factors like clarity, cut and size equally makes a ruby valuable."

Sapphire, the precious gemstone, belongs to the corundum group. It is available in different colours like blue, green, purple, yellow, brown, white, pink-white, etc. All colours except red are found in a sapphire and a red sapphire would be a ruby.

Emerald is the precious stone belonging to the BERYL group. It is available in green (bright green, yellowish green), deep red (due to presence of chromium), Black emerald, though rare, is found in Pakistan. The black effect is due to total internal reflection. Emerald is commonly found in Colombia, Siberia, Russia, South America, Pakistan and India.

Pearl is an organic gem found in white, yellow, gray, purple, pink, blue and black colours. Persian Gulf, Red Sea and Indian Ocean are the main source for pearls. It is "used as found". No cutting or polishing is done on them, just a hole is drilled or pierced. Pearls are of two types, namely fresh water pearls (which have a wide colour range and have thick layer of nacre) and cultured pearls (which has a thin layer of nacre)