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Precious stones are minerals with particular qualities: BRIGHTNESS, TRANSPARENCE, COLOR, HARDNESS, OPTICAL ILLUSION, and SPECIAL INCLUSIONS.
Only few materials are considered precious: PEARLS, CORALS, AMBER.
The development of precious stones is strictly connected to the minerals one; rocks are made up of one and/or more minerals, which are chemical inorganic substances with a homogeneous chemical composition. The most important employment of precious stones is in the jewelry. The first stones which were employed for jewelry or decorations or common use, were AMBER, GARNET, ROCK CRYSTAL, NEPHRITE, AMETHYSTE, JADE, ESMERALD, PEARLS, CORALS, and others less common. Nowadays modern technique uses many types of precious stones for different purposes. BERYLLIUM is employed for atomic physics in order to slow down neutrons. ROCK CRYSTALS are employed for heading airwaves and they are also producers of oscillations of radar devices and supersonic ones. Instead, SAFFIRE is employed in gramophone, in order to change mechanical movements in electrical pulses. CORUNDUM is used for watches and precision utensils.
Hardness of a precious stone can be simply determined thanks to Mohs' hardness scale.


In Mohs' scale the level of hardness increases from the top to the last level. As a consequence, talc is the softest mineral, whereas diamond is the hardest. Gems must have a high hardness level in order to last long time. Hardness level is tested by placing a sharp point of one specimen on an unmarked surface of another specimen and attempting to produce a scratch, so topaz scratches quartz, hence the first one is harder than the second one.


Hardness level: 10
Diamond is the hardest gem stone which is known by man. It is made up of carbon as lead in a pencil, but the melting point is 4000 degrees (6900 Fahrenheit degree).
A diamond can be classified by four important characteristics:
  • CUT

Color classification is made by using "master stones scale" under an artificial standardizes light.
Diamonds color graduation scale

D E F G H I J K L M N O P Q R S==> Z


Letters D-E-F-G are considered diamonds for collection or investment, whereas the ones used in jewelry are letters H-I-J.
Exceptional white D River
Exceptional white E River
Rare white F Top Wesselton
Extra white G Top Wesselton
White H Wesselton
Slightly dye I Top Crystal
Dye J Crystal
CLARITY A diamond can be considered without imperfections only if it is found without any inclusions or inside characteristics after an exam with a hand lens at 10 powers. Clarity of a diamond can be classified using other parameters such as dimensions, position, brightness and the number of inclusions. Outside characteristics and structure phenomena can be pointed as "identification signs" or "comments". The ground-level of clarity pointed by the scale (indicated with letter p for piqué) is referred to visible with naked eyes by a qualified person.
IF VVS 1 VVS 2 VS 1 VS 2
SI 1 SI 2 I 1 I 2 I 3


I F Internally flawless internally flawless no inside flaws visible at 10x
V.V.S.1 Very Very Slight inclusions very difficult to identify with hand lens at 10x
V.V.S.2 Very Very Slight inclusions very difficult to identify with hand lens at 10x
V.S.1 V.S.2 Very Slight nclusions difficult to identify with hand lens at 10 xs.
S.I.1 S.I.2 Slightly Iimperfect imperfect inclusions and outside flaws easy to identify with hand lens at 10 xs.
P.1 - I.1 Imperfect inclusions and flaws very easy to identify with hand lens at 10 xs.
P.2 - I.2 Imperfect inclusions and outside flaws easy to identify with naked eyes.
P.3 - I.3 Imperfect evident inclusions easy to identify with naked eyes.


Type of cut: brilliant cut, marquise cut, drop diamond cut, heart cut, oval cut, octagonal cut or emerald shaped diamond and princess cut. Round brilliant shaped diamond has 58 facets: there are 33 facets on the upper side (or crown) whereas there are 25 of them on the lower side (or pavilion).

A - Crown
B - Corner (more than 34°, lesser than 41°)
C - Crown
D - Total height 61.7%
E - Table 55 - 57%
F - Girdle diameter
G - Ppavillion facets
H - Main pavillion
I - Pavillion 43%
A - Pavillion facets
B - Girdle
C - Table
D - Star
E - Crown main facets
F - 100%
G - 55 - 57%


Hardness: 9
Chemical composition: Al2O3
Crystalline system: triangular shaped
Index of refraction: 1, 76-1, 77
Sapphire is a type of corundum. The blue color depends on the presence of tiny amount of iron atoms and titanium in the crystal lattice of aluminum oxide (the color blue can varies from light blue and dark blue). The hardness is the same of the ruby's one (that's another feature of corundum), whereas fluorescence is not the same for all varieties which depends on the color and on the origin deposit.
A ray of light, which seeps in the stone, will be divided in two rays. This phenomenon is called birefringence or double refraction. Due to this phenomenon, every object, which is watched through the crystal, will appear slightly slipped. This feature is the same in every gem stones belonging to dimetric group. The fact, that there are only two rays, affects the color giving to it different shades. This chromatic different effect is called dichroism. The most pleasant color is real deep blue.
The gleam of sapphire is vitreous, but sometimes it can tend to adamantine. The value of light dispersion is more humble than the diamond's one, hence the beauty of corundum is not in flash of color as in the diamond, but in shades of color.
As it is told before, due to the presence of metal oxide in the crystal, these gem stones have wonderful colors; in fact the beauty of these is not clarity but colors. Thanks to inclusions is possible to appoint the origin.
Star-shaped gem stones are one of inside features of corundum. Because of that feature, these stones are cut as cabochon cut, so it let the reflection of some inclusions which make on the surface some rays of light as star-shaped.



Hardness: 9
Chemical composition: Al2 O3
Specific weight: 3, 9- 4, 1
Crystalline system: triangular shaped
Refraction index: 1, 76- 1, 77

In 1800, ruby was recognized as a corundum variety, as sapphire was. The finest color is dove-red: it is pure red with some bluish shades. Color distribution is often irregular: both stripes and spots.
Chromium gives red color to the gem stone, but iron gives bluish shades. Red color changes due to the different veins from which it comes from, but in any case it is not useful for establishing the origin, because in every vein there are gem stones with all possible shades. Marble of the dolomites is the principal a rock from which ruby comes from, but the amount of this mineral is too modest in those veins to take commercially advantage. Mining is usually made in alluvial veins. Thanks to the high specific weight, ruby is extract from gravel and rivers and washing, and then it is separated from the achieved concentrate by hand.
Rough ruby has rounded-off corner and rough gleam, whereas when it is cut it is nearly glossy as a diamond.
If it is looked with a hand lens at 10x, it is possible to notice many inclusions which underline the natural origin and they let to recognize the ones of synthetic origin.
If a ray of light passes through a ruby, it will split in two rays. This phenomenon is called birefringence or double refraction. Due to this phenomenon, every object, which is watched through the crystal, will appear slightly slipped. This feature is the same in every gem stones belonging to dimetric group. The fact, that there are only two rays, affects the color giving to it different shades. This chromatic different effect is called dichroism. The most pleasant color is deep purple red.



Hardness: 7, 5-8
Chemical composition: Al2 Be3 (Si6O18)
Specific weight: 2, 8
Crystalline system: hexagonal shaped

With aquamarine, emerald belongs to beryllium of which there are other varieties of different colors. Emerald is the finest of varieties: his green color has not any comparisons. The chromium is the substance which gives the green color, but also vanadium. The color is stable both for light and heat, but it change at 700-800°. Only best varieties of emeralds are transparent because, due to inclusions, it can be translucent.
The more is green color fine, the more the value of the stone will be. It will be also a higher value than any other pale stones, even if it is pure. Color distribution is often irregular, arranged as spots or stripes. In general, gleam is vitreous.
The mainly used cut is the one called emerald-cut: it is a rectangular multifaceted shaped with rounded off corners and even facets. Other all shapes are used. Cabochon cut is used when there are fractures and much defined natural inclusions.
In order to look inside emeralds, it is necessary to use a 10 power hand lens. Inclusions are not flaws but they establish the natural origin of the gem stone. Inclusions help also to recognize from synthesis and other fakes.



Hardness: 7,5-8
Chemical composition: Al2 Be3 (Si6 O18)
Crystalline system: hexagonal system
Refraction index: 1,57
Aquamarine is a variety of beryllium. Cut aquamarine are usually thermally treated (aquamarines heated at more than 400° get intense everlasting blue color). Aquamarines are used for extraction of beryllium, for gemological and decorative field, for collecting market and eventually for crystal-therapy. Hardness, origin and color are considered the bases for classifying aquamarines for matrix. In spite of aquamarine is considered the commonest mineral which supplies blue-chip precious stones, those minerals have charm and color which make them unique.



Features: pearls belong to organogenic gems because they are produced by mollusks and rarely by gastropods. Pearls are made up of mother-of-pearl, which is composed of calcium carbonate and an organic substance which bonds micro crystallines. Micro crystallines develop in a concentric way. Although pearl's hardness is between 3 and 4, they can be considered extremely tough and it is really difficult to break them. Their size varies between from a pin-head and a pigeon's egg. The typical optical illusion, called "oriental effect" (technically called iridescence), depends on the distribution of overlapping layers of calcium carbonate and conchiolin on the surface of the pearl. Colors of peals change depending on both the mollusk which has produced it and on the type of water in which the mollusk lives. Coloring, also depends on the color of the surface of overlapping conchiolin layers. Conchiolin is an organic substance, so if it dries it can change: as a consequence, pearls become lackluster for first, and then they break and lose the first layer. A correct preservation with periodic re rehydratation can help to stretch pearl's life. Exsternal conditions of humidity and aridity are dangerous for pearls. Pearls are sensitive to acids, sweat, make-up, and hair-spays.



Mother-of-pearl is a valuable material which is proceed by the inner of shells of some mollusks such as oysters of iridescent pearl-like color. It is used for producing many objects because of its hardness. It is also used for decoration of some surfaces.


Hardness: 7
Chemical composition: SiO2
Specific weight: 2,6
Crystalline system: Triangular shaped
Refraction index: 1,55
It is a violet variety of quartz and it is characteristic of Baltic rocks. Since 3000 a.C., it was one of the most valuable precious stones used for jewels in Egypt and Mesopotamia. Nowadays it is still one of the most appreciated gem stones. The word amethyst comes from Greek and it means "Not drunk: this stone was supposed to be the defender from drunkness and it was brought as an amulet. According to Christian mythology, it was supposed to be the symbol of wine on the altar. It is usually set on mass goblets as decoration or as solitary precious stone on the ring of bishops.



Hardness: 8

Chemical composition: Al2 SiO4 (FOH)2

Specific weight: 3,5-3,6

Cristalline system: rhombus shape

Index of refraction: 1,6

The commonest topaz can be yellow, light blue, pink or uncolored.  The ones uncolored have a particular brighthness, due to that feature, they called “pingas d’agoa” in Brazil (drop water). The name topaz comes from the Sanskrit language “tapas” which means fire and heat.

One of the biggest topaz (1680 ct.) is called “Braganza” and it is set in the Portuguese crown.


Hardness: 5-6
Chemical composition: CuAl6(OH)8(PO4)4 4H2O
Specific weight: 2,6-2,8
Crystalline system: triclinic shaped
Refraction index: 1,61
Due to the presence of copper, the turquoise color varies between intense blue and green light blue. There are many black and brown veinings because of iron oxide inclusions or the mother rock. Turquoise is often cut as cabochon cut for rings and necklaces.



Hardness: 6,7
Chemical composition: (MgFe)2 SiO4
Specific weight: 3,3-3,5
Crystalline system: rhombus shaped
Refraction index: 1,6-1,7
Peridot is also called "Olivina" (olivine is an Italian word which means little olive) due to its olive green color and for its oily brightness or chrysolite, from Greek chrisosoro, lithos-stones. it's difficult to find large-in-size peridots, in fact they are rather rare and they are valuable for their yellow and green color.



Hardness: 7
Chemical composition: SiO2
Specific weight: triangular shaped or amorphous shaped
Refraction index: 1,55
Agate is am amorphous shaped quartz, and it the most common gem stone. The name agate comes from the Greek word acates, which was used for labeled river Dirillo in Sicily, from which Greeks extracted the stone. Agate is made up of different layers or colored stripes clearly demarcated. These colors are usually grey, white and liver. The layers surround the central zone as lace. The central zone is made up of amethyst and rock crystal. It is often discovered in ancient excavations because it was usually set in jewels. The agate was used ad seal or it was also worked for little pots for perfumes and dyes. Even necklaces with agates were appreciated as decoration objects.



Hardness: 7
Chemical composition: SiO2
Specific weight: 2,6
Crystalline system: triangular shaped
Refraction index: 1,55

Hyaline quartz is in the form of uncolored crystals which are as clear as water. The name comes from the Greek world kristallos which means ice. This stone was supposed to be extremely harden so it could not melt. During the following centuries, it was supposed to be able to divine future in rock crystal sphere. Nowadays, rock crystal are used for necklace and artistic objects.



Hardness: 7
Chemical composition: SiO2
Crystalline system: triangular shaped
Refraction index: 1,55
Citrine quartz is wrongly called topaz in jewelry. The citrine is a macro crystalline quartz and the color varies between yellow, red-yellow and brown.



Hardness: 7- 7,5
Chemical composition: XY3Z6(OH4)(BO3)3/Si6O18]DoseX=Na,Ca;Y=Mg,Li,Fe;Z=Al, Fe, Cr
Specific weight: 3-3,2
Crystalline system: triangular system
Refraction index: 1,62-1,64
Tourmaline is one of the most popular mineral gem stone in the world.
It can be found in every color varieties in every continent, from pink to green, red, blue, purple and black.
During ancient times, this stone was supposed to help people to get sadness and traumatic memories over and to release love energy, happiness, and inner harmony.



Hardness: 7-7,5
Chemical composition: Mg2 AL4Si5O18
Specific weight: 2,5-2,6
Crystalline system: rhombus shake
Refraction index: 1,542
Iolite is a light blue variety of cordierite: as synonymous of cordierite it can be used also croite. This stone is famous for its pleochroism: if it observed from three different perpendicular directions , to be more precise the ones of crystalline axis, it is possible to identify three colors: light blue, grey light blue and yellow, thanks to light absorption.



Hardness: 6,5-7,5
Chemical composition: X3Y2(SiO4)3-dove X=Ca,Mg,Fe,Mn;Y§=Al,Fe,Cr
Specific weight: 3,4-4,6
Crystalline system: cube shaped
Refraction index: 1,70-1,90
The word garnet comes from Latin granum which means wheat, however it seems that Romans referred the name to pomegranate in place of wheat, in fact when the pomegranate is ripe, it has inside some red seeds which look like galore precious stones. It is a popular gem stone. Depending on the chemical composition, it can be of different colors and the most famous varieties have names like: pyrope (from Greek pyropo which means "looks like fire") which is dark red, Glossular which is salt and aluminum silicate of lackluster green of emerald green and finally Rhodolite of variable color between pink and lilac red.



Chemical composition: zirconium dioxide (ZrO2) with yttrium oxide (Y2O3)
Crystalline system: cube shaped
It is produced in laboratory, and it is transparent and uncolored. It is usually cut as diamond shaped. A skilled eye can easily recognize it with a hand lens at 10x. There are different tonalities of this stone, such as green, violet, yellow, red, blue, black, light blue and pink orange.
It seems a diamond but it has a much less value than it. It is used for cheap jewelry.



Enamel is a mass of art and techniques. His name comes from the German word smaltjan (in modern German it's schmelzen) which means to smelt. Up to Middel Age it was called with the Latin world vitrum which means glass and for for long time it was also called glaze. Enamel is made up of a mixture of silicates: silicon dioxide, soda, quartz, red lead, borax, feldspar, phosphatic minerals. There are about 700 different colors of enamels, although it is possible to combines many different shades with layering technique of the different colors.



Silver can be found in nature either pure or in the form of minerals. Its symbol is AG (from Latin argentum).
It is a ductile and malleable mineral just harder than gold. Silver is also one of the best thermal conductor. The color is whiter than gold and his oxidation number is +1 and the atomic number is 47.
Silver is highly employed as precious metal (MARK 925), otherwise it is employed for mirrors production, photography (black and white photos), coins, cutlery production, odontology and for the production of long-lasting batteries.



GOLD IS THE PRECIOUS METAL PAR EXCELLENCE. At pure start (gold title 1000/ooo), it is very malleable and ductile and so it is not very suitable for goldsmithing. Due to this particularly feature, it is alloyed to other metals in order to award hardness and resistance necessary for malleability.
BY LAW every alloys must be enrolled in a specific list which is universally recognized. Alloys are enrolled according to the percentage of gold in the alloy. In the table below there are the commonest gold alloy with the respective spread in some countries.

Purity thousandths Carats in purity Countries
1000 24 some countries in south-east Asia
916 22 some Arab countries
800 19 Portugal
Italy, France, USA, United Kingdom
585 14 Italy, USA, Mexico, some east European countries
417 10 USA
375 9 Italy, United Kingdom
333 8 Germany

The gold alloy usually employed for jewelry is white gold alloy 750 thousandths (which means: 750 parts of pure gold per 1000 parts of the alloy.). It is a very resistant alloy and it is usually covered with rhodium plating and the end of the manufacturing process, in order to give brightness and gleam.



It is a precious metal (maybe it is more precious than gold because it has a quotation about 3 times of the gold's one). Although its employment in jewelry is limited to the galvanic rhodium plating of white gold alloys.
White gold alloys have not a shiny and white aspect , if they have not rhodium plating, in fact they have a yellowish and lackluster look. The process is called "rodiatura" and it consists of applying a thin coat of rhodium by a galvanic bath (1micron=1 thousandth of millimeter). It will award glean and brightness to the jewel, the one that everyone is in the habit of seeing in the shopping-windows.
By the way, it is necessary to repeat the galvanic bath, in order to preserve the gleam and the brightness of the jewel, because sweat, friction and the time tent to remove the layer of rhodium which was applied.

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