The associations of the gems to the zodiacal signs are the result of a search of mine carried on the web sites and several Astrology magazines. That’s why you may find some inaccuracies. But I can assure you, on the whole, that what is written is more or less close to reality.
Diamond is associated with the Lion sign, ruled by Sun. It instils energies and support to health, relieving nervous stress and cleasing our organism of too many toxins. Diamond owes its name to its hardness in Greek "adamas" means indomitable. It's for sure the gem presenting exceptionally beautiful optic effects and for this reason is considered the Queen of the gems
Ruby owes its name to its red colour from the latin "rubeus". Ruby is a variety of corundum. Its colour is often irregular and can be better distibuted by means of a thermal process. Inclusions are frequent. They don't lessen the quality: on the contrary they prove the naturalness of the gem. Ruby is associated to the Scorpio sign, ruled by Pluto.It protects you from all negativities, physical injuries and diseases.
Emerald is associated to the Taurus sign, ruled by Venus. It prefers green colour, and what's more it'll bring you love, balance and understanding. It's also useful in healing sight problems. Emerald comes from the grek " smaragdus ". It belongs to the beryl species. Its green colour is incomparable, that's why the word emerald green is also used outside of Mineralogy. Like ruby it presents inclusions "only the best quality is trasparent". They are not considered faults ( providing they are not many ), but always prove the naturalness of the gem.
Sapphire comes from the greek " saffeiros" which means blue. Its fluorescence is not the same for all varieties. It dipendes much on the colour and the field of origin. Sapphire is associated to the Virgo sign, ruled by Mercury. It helps to direct energies and love to anyone who needs them.
Aquamarine is associated with the Pisces sign, ruled by Neptune. This sign prefers anyway the blue stones. They increase its vital force. Aquamarine also is a variety of beril. Its name is due to its "water blue colour". The most precious quality has deep blue colour, is a very fragile but unlike the emerald, it has more regular distribution of the colour.
The name Opal comes probably from the sanskrit "upalas" precious stone. Opals are divided into three groups: the Noble Opals with their typical plays of colour, the Opal of Fire red and yellow in colour, and the Common Opals very common because they are usually opaque and without any plays of colour. Opal is associated with the Cancer sign and is ruled by Moon. It prefers all white colours. Their function is to soften, calm and bring balance.
Amethyst is associated with the Pisces sign, ruled by Neptune. This sign, being very sensitive, needs Amethyst for protection, steadiness and to banish melancholy. Amethyst is the most precious stone of the quartz group. It comes from the greek "améthystos" and means anti-inebrating and it's said to have supernatural powers. This quartz is also rich in traditions ( in the Roman Church bishops usually wear a big Amethyst in the episcopal ring ).
Only the calcareous branching of Coral is used in jewellery. It forms by the action of small polyps scattered in the tiny cavities of the soft pellicle which covers the calcareous ramification. The most precious is the Noble Coral "corallium rubrum". Coral is associated with the Aries sign, ruled by Mars. This stone gives the sign strength and energy.
Pearl is always associated with the Cancer sign, ruled by Moon. It prefers all white and milky stones. Pearl is said to soften, calm and bring balance. The name Pearl comes probably from a kind of shellfish called from the latin "perna". Pearl is produced by shellfish, made of mother of pearl, which is mainly calcium carbonate and organic substance, the ligand among the microcrystalls which develop in concentric circles starting from a little central area.
Tormalines present a wide range of colours, larger than any other gem. They are classified according to their colour and it's difficult to find one with a uniform colour. Originally they were called with a singhalese name "turamali". Probably because of the extreme variety of their colous, I couldn't find any association with a zodiacal sign.
Lapis lazuli also hasn't got a particular position within the zodiac but can be associated to all those signs which prefer the blue colour. Lapis lazuli comes from the medieval latin "lapis làzuli" which means blu stone. Many scientists don't consider it a mineral, but a rock. The colour is uniform in the best quality, but generally is spotted or streaky.
The name Jade comes from the spanish "piedra de la ijada" which means stone of the loins because it was used for renal diases in Central and South America. It's distinguished into two minerals: Jadeite and Nephrite. It comes in different colours. As for the first one, the most precious is the Imperial Jade, emerald green in colour, the second one is Green. As for Jade I coudn't find a specific position in the zodiac because of its many colours.
For its green colour Olivine can be associated with the Libra sign since this sign, ruled by Venus, prefers the green colour. Olivine, more commonly called Peridot, draws its name from the olive green colour of its crystals. The greek name for it was "khrisólithos" which means golden stone. It has a vitreous and oily schiller. The dark stones can be lightened if brought to incandescence.
Moonstone belongs to the Felspar group. Its name is due to the white bluish reflection originated by its structure. It is cabochon cut. Moonstone, alike pearl, can be associated to the Cancer sign which is ruled by Moon. Moonstone is particularly suitable for women wishing to get pregnant or to raise their femininity.
All iridescent and yellow stones are ascribed to the Gemini sign, ruled by Mercury. Suitable to this sign is therefore the Yellow Topaz, which has the function to control emotivity and to stimulate spirytuality. Topaz can be found in different colours, of which the most frequent is yellow, the most precious pink. The coloured stones are step cut, the colourless ones diamond cut, those with many inclusions are cabochon cut.
The name Turquoise means "Stone from Turkey", because that was the country from which it was imported to Europe. Its colour is blue and it's quite rare to find it uniform; usually you find it with brown spots of limonite or dark grey of sandstone or black of jasper. Turquoise is associated with the Sagittarius sign, which ruled by Jupiter, prefers the blue colour. This stone has a typical function of protection an guarantees vitality to all the body.
Red Garnet is associated with the Aries sign, ruled by Mars. It prefers all the stones ranging from red to purplish-blue. Garnet brings strength and energy. Contrary to what it is thought Garnet comes in different colours but all with the same chemical composition. The most common anyway is the red one. Its name comes from latin "granum" and it's due to its rounded shape. It can be distinguished into two categories Ugrandite and Piralspite.
Quartz can be found in different colours and it's certainly one of the most common minerals in the world. Its gems are the most copious. in transparent stones purity is almost absolute. Use of quartz is very ancient, same as human history. Blue quartz is associated with the Aquarius sign, ruled by Uranus. It prefers all the colours ranging from blue to purple and black. Quartz helps to put thoughts into order and clear the mind.
With Capricorn, ruled by Saturn, are associated dark and black stones. Typical stone of this sign is Onyx which helps those bom under this sign to overcome possible difficulties, by stimutating them all the time to realize their own individuality, and regularize sexual impulses. Onyx from the greek "onis" which means nail, has taken this name because, like the nail, is translucent. Onyx is a chalcedony of a single colour.