Below various gems & stones are described with their effects on human body. To know in detail one can go through the book written by Dr. D. Koley.
Gems plays a very important role in the human body. Human body is comprised of the seven spectrum colours. Whenever there is an deficit of the spectrum rays in the body it leads to the physical disturbance. So the gems are predicted in that way. Like when there is a deficit of blood that means there is a deficit of sun-rays, so ruby or red-coral are adviced. Similarly due to the deficit of cold-rays cold gems like pearl are instructed to wear. But the first and foremost thing that is required for physical balancing is to wear the gems in appropiate quantity and the gems should be real and of good quality. To get a brief knowledge about the gems you can go through the gems section discussed below or you can go through the book 'Gem-the Healer' by Prof. D. Koley worth $ 8 / £4 only. Available by Post. Add $5/- as postal charges.

RUBY (Chuni)  Ruby is a red colour precious stone that ranks second among the precious gems in the World. The colour of the stone varies from deep-rose red to light red. It is a common belief that Ruby helps to subside disorder of winds, bile and phlegm. It also relieves ulcer, eye disease and pain in the body. This stone also act well upon bones, nerves, heart, lungs & brain. It also helps to increase seminal and internal power of man and keep a physiological balance of the body. It is composed of Alumina 97.32 and Iron Oxide 1.09, Silica 1.21. The hardness of ruby is 9. It is found in Burma, Ceylon, Siam (Thai), Arizona, New Mexico and India. Ruby of Burma that is red like pigeon blood is 'The Best' and is rated as first class in the World. It is given as a remedial guard for Ravi (Sun).
 PEARL (Moti)  Pearl claims an adorable place among ladies is a precious gem that stands 3rd among the world though it is not a mineral product. It is termed as 'sukti' in Sanskrit that means 'Oyster'. According to Hindu mythology when dewdrop fall on Oyster shell during the period of sun under the swati-nakshatra, which in course of time develop into a hard pearl in the bed of ocean. According to the dewdrops falling on different animals it can be classified into different groups like 'min'-moti, 'gaja'-moti, 'sankha'-moti, 'bheka'-moti, 'sarpa'-moti, 'baraha'-moti, 'vamsa'-moti. Pearls are available in the Arabian Sea, Bay of Bengal, in Ceylon, Bombay, Japan and Australia. Black pearl are found in Mexican Gulf. Now pearls are artificially cultivated. The pearls can be divided into four classes according to their shape colour and quality. They are Brahman, Ksatriya, Vaisya, and Sudra. According to the formation of pearl it is stated as 'male or 'female'. It is composed of calcium carbonate for which it is highly sensible to acids. The specific gravity of a pearl is 2.5 to 2.7 and its hardness is 2.5-3.5. According to the astrologers the pearl give a guard from the moon, which is affected of malefic or at a debilitated house. It saves from physical trouble and mental disturbance. Pearls even bring some disaster to the person if they are defective. Useful pearls are invariably white, weighty, big and clean on the surface and mildly bright with a balance round shape. Pearl is effective in curing certain diseases like skin troubles, mental problems, female diseases etc. It also keeps the temper of the person cool.
 CORAL (Praval) Coral is a perpendicular or right-angled or square-shaped, oval sea-gem. It is formed due to gradual accumulation of fossilized skeleton or secretion of the polyps (red coloured sea worm) in layers. It has no mineral contents. It has various colours like light yellow, white, red or pink-rose. It is found in the Sea of Japan, in the Mediterranean, Tunis, Morocco, Algeria, Corcica, Sardinis, Napples and France. Bluish Coral are found in the western coast of Africa and a type of blackish coral is found in Persian Gulf but Italian Coral is worldwide famous. Now costly red-rose coral is found in Japan also. Its specific gravity is 2.6 to 2.7. It is soft and highly polished. When it looks like rising sun it is called Brahman Coral. The red-rose and hard corals belong to ksariyavarna caste. The less bright red coloured coral with tinted yellow is considered as Vaisyavarna. The blackish coral are Sudravarna. Now a days artificial corals are readily available in the market, which are made of bakelite or galaleath plastic. It is used as prevention against diseases like asthma, blood dysentery, blood defects, cough, constipation, gall (bilious trouble), indigestion, leucoderma, anaemia, ulcer, urinary disorder, female diseases particularly in case of haemorrhage. It also acts very prominently regarding family problems. It is given as a protection against the 'Mars' when it is retro grated or in a disturbed position.
GOMED (Zircon) Gomed is mineral gem, tetragonal crystal used to minimise the malefic influence of Rahu. It is available in Ceylon, some parts of Himalayan range, The Deccan, France and South Africa. In Ceylon gomed is well known as 'Matura-Diamond'
It is constitute of Zirconium, sand, and oxygen being chemically mixed up. Its specific gravity varies from 4.0 to 4.7 and the hardness is 7.5. It can be divided into four categories. White, weighty, transparent gomed are termed as 'Brahman'. 'Ksatriyavarna' gomed is deep blood red in colour. The deep yellow coloured gomed is called Vaisyavarna. The bluish gomed is Sudravarna gomed. It is compulsory to examine gomed before use else faulty once can bring disasters.
 YELLOW SAPPHIRE (Pokraj)  English topaz is known as Pusparag or pokraj. It is a gem stone and falls in a particular group of minerals. They are of several colours like white, pale blue, honey coloured or of amber coloured having many shades like pale-green, reddish or wine yellow. The white sapphire are rare where as yellow one is easily available. The yellow sapphire tinted with the reddish colour is very costly and is mostly found in the Himalayan Region. Specific gravity is 3.4 to 3.5. It is hard and made of lithium, aluminium and sands. It is available in Ceylon, Red Sea, Japan, Burma, Madagaskar, Africa, Brazil, Germany, Siberia. The Burmese topaz is 'The Best'.
According to the variation of the colour it can be classified into
1. Deep yellowish.
2. Slight yellowish tinged with red
3. White
4. Water-Coloured
5. Deep blue
6. Light blue.
It is used as a save guard against Jupiter. It influence prosperity, providing one with enough of good things. It prevent the malefic influence to some extent.
BLUE SAPPHIRE (Nila)  It is regarded as the best gem in the ancient India. According to the Purana blue sapphire has its origin from eyes of the Valasura. With the variation of colours it can be classified into four categories. White sapphire are considered as the Brahman, the red sapphire are the Ksatriya, the yellow are the Vaisya and the black are the Sudras by class. It is composed of Aluminium Oxide. Its hardness is 9, specific gravity is 4.06. It is found in Burma, Kashmir (India), Ceylon, Thailand, Pennsylvania, Georgia. It prevents the diseases caused by wind, bile and cough turned malignant. It also relieve the person suffering from epilepsy and mental disorder, paralysis, hysteria.
EMERALD
(Panna)
A piece of perfect emerald is flawlessly deep green, shining, transparent and seems to be full of gold-rust within. It radiates upon other things placed close by at the fall of sunrays upon it, Emarald of glass-green colour is rare and sometimes, it is costlier that diamond and ruby. It is very much similar to aquamarine. Structure of the emarald is hexagonal. It is harder than crystal and softer than sapphire. Its specific gravity is 2.4 and the hardness is 7.5 to 8. It consists of silica, alumina, magnesia and sodawater. It is very much brittle. It can be divided into three divisions according to colour and nature- Brahman (Bipra), Ksatriya, and Sudra. It is found in Brazil, North Carolina, Australia, South America and Russia. Good quality of emerald is found in Columbia. It gives protection against conbust Mercury. People suffering from stomach trouble, dyspepsia, dysentery get much benefit from this gem.
 CAT'S EYE (Lasunia Zuza)  It is a precious mineral gem and it resembles a cat's pupil that glares in darkness. It is rare variety of chrysoberyl. It has got a remarkable brilliance that moves over the surface of the stone. It is available in the different parts of India, but the Ceylonese one is 'The Best'. It is brittle, and not damaged by any chemical. It is composed of Glucina 19.8, Alumina 80.2. It is of different colour - white, bluish or tinted bluish, ash-white, honey-like and it has got varityof shades. There are four type of Cat's Eye
1. The first one is golden (Kanakksetra). It has white moving lining of brilliance on of the surface is very costly.
2. Second one is light yellow coloured has moving brahmasutra.
3. Third is the blakish (Shyamksetra) and sometimes greenish also. It even has moving brahmasutra.
4. Fourth one is Dhumravarna cat's eye. It even has moving brahmasutra but is not so dazzling.
The effect of the gem depends upon the brightness. It give the safe guard against Ketu.
DIAMOND (Hirak) Diamond is one of the most percious stone in the world. It is a hard type of stone and its lusture abnd the power of reflection is wonderful. It is available in Kimberley, South Africa are bigger and better in size and quality. It is even found in Brazil, California, Arizona and Australia. It is purely a carbon product. It may be tgransformed or non-transformed in nature. The specific gravity is 3.52 and reflective index is 2.41. Its colour varies.
GARNET (Pulakmani)  It is an attractive gem, which is a common crystalline form of cubic system, is a mineral product. The red species of garnet, termed as pyrope garnet is purchased by the people as cape ruby. It is found in various colour: orange, light yellow and light green are termed as hessonite, topazolite, demantoid respectively. Hessonite is found in the mountainous region of India, Ceylon, Brazil, Australia and America abundantly. The specific gravity of Garnet is 3.6 and 3.8 and hardness is 7.25.
Yellow garnet is used to protect from malignant and green garnet increase intelligence and bring peace in the family.
AMETHYST It is a purple coloured stone. In India it is termed as Sandhyamani. According to the colour variation it can be categorised into four distinct divisions. Previously it was of only two divisions:
1. Oriental Amethyst of violet Sapphire is a form of Corundum
2. Occidental Amethyst of True Amethyst is a form of quartz.
The amethyst give a great relief to the people suffering from headache and eye-trouble if it is wear in correct size and weight. Its specific gravity is 2.65. It can be found in Brazil, Mexico, Canada, Spain, Madagaskar, China and Siberia.
TURQUISE
(Phiroza)
Phiroza is adored by the Islamic world as " Fortune Stone". Its real colour is greenish-blue. The Egyptian Phiroza is deep blue in colour. It is found in Turkey, Arab, Persia, China and Australia. It is often used as a substitute of Panna.
OPAL  This is a non-crystallized costly stone with a smooth surface. It is formed of sandstone due to the solidification of the melted sand under the earth. In the material constituents of Opal there 6% to 10% of water. It radiates variety of colours by sunlight.
There is different type of Opals
1. Fire Opal - not bright
2. White Opal - bright and send out blue, green, red lustre
3. Black Opal - seven colours are put into display in it.
4. Water Opal - transparent type cheap opal having different lustre.
Opals are found in Mexico, Ireland, Arabia and Ceylon. It gives mental peace.
TOURMALINE  It is secondary gem of green, blue and yellow colour. The Brahmamani type of Tourmaline is of rare type. It is half green and half rosy or it is red in colour. It is found in India, Ceylon, Burma, China, Siberia and Brazil. Black one is only found in Burma. It is compound of twelve elements, which contains alumina and iron and other matters mixed with sandstone and alkali as its components. It is almost equal to quartz in hardness.
LAPISLAZULIS  It is kind of blue or a little reddish non-transparent marble has a smooth surface. It is remedial for liver trouble. It is very cheap and is found in Afghanistan and Chile. It is often used instead of Cat's Eye.
AQUAMARINE It is a green coloured transparent, beautiful gem. It is famous as Varupmani in India. It brings happiness in conjugal life and helps people in competitive works. It gives relief in Urinal Trouble. It is found in Brazil, Siberia and America.
PERIDOT It is a secondary gem of light and deep green colour. In English it is termed a Bottle-Green Gem. It elevates hostility or disagreement between the husband and wife. It is a cheaper gem is composed of silica, iron and magnesia. It is worn instead of Panna and Cat's Eye. Peridot is found in Queens land. Burma and Ceylon.
AGATE It is found in blue, red or in black colour in Brazil, Australia, Russia, Germany, and India etc. It helps to regain health and even bring success in a lawsuit.
ONYX It is a secondary black non-transparent gem. Its natural colour is green so it is used instead of emerald. It is found in the southern part of India, Mexico, Brazil and America.  
JASPER  Red jasper benefits a person in lungs trouble
JADE It is a black type of gem gives relief in kidney trouble.
ZIRCON  It has various colours like white, black or rosy. It gives relief in cough, cold and seminal trouble
BLOODSTONE  It is a secondary gem having red spot on greenish body. It helps person suffering from dyspepsia and stammering. It is found in Brazil, America and Egypt.
QUARTZ  It is a transparent and costly gem with a variety of colours like black, yellow, brown etc. It helps to alleviate eye-disease and effects of blood poisoning. It can be found in Madagaskar, Brazil and Russia.