Ruby

Ruby = Al2O3 aluminium oxyde
Hardness = 9
Color = red in various shades
Ruby owes its name to the red color (lat.Rubeus).

Only around 1800 was it discovered that, together with sapphire, ruby ​​is a variety of corundum. The mineral that gives the ruby ​​color is chromium and for the brown colors, also iron. The color differs from the origin, even if in each deposit there are stones with different shades. The most prized color is the so-called “pigeon blood” (a pure red with a bluish tinge). Color distribution is often uneven: banded or mottled. Heat treatment is usually used to enhance the color. Inclusions are frequent.
They never constitute a reason for a decrease in quality, but are evidence of the natural origin of the stone and allow it to be distinguished from synthetic stones. Inclusions of rutile needles give a slight “silk” glow. If the stone is cut appropriately (cabochon) they give rise to an effect called (chastity) or (asterism).

The only significant deposits are in Burma, Thailand, Sri Lanka and Tanzania. The most important are in northern Burma, near Mogok. Only 1% is found in gem quality. Large stones are very rare.

Thai rubies typically have more brownish undertones and are found in the Chantaburi district, southeast of Bangkok. In Sri Lanka the deposits are located in the vicinity of Ratnapura, and their color ranges mostly from light red to raspberry red. In Tanzania since the 1950s zoisitic amphibolite has been extracted which also contains rather large rubies, but almost always opaque. Only a few specimens are suitable for cutting.

Minor deposits are in Afghanistan, Australia (Queensland), Brazil, Cambodia, Kenya, Madagascar, Malawi, Pakistan, Zimbabwe and the USA (Montana and North Carolina). Small deposits of ruby ​​and sapphire are also in Switzerland (Canton Ticino) and Norway.

Emerald

Color = emerald green, light green, yellowish green, dark green
Hardness = 7,5 /8
Composition= Be3Al2(Si6O18) beryllium silicate

The name emerald derives from the Greek (smaragdos), but perhaps dates back to the Persian or ancient Indian period. It means “Green Stone”. The emerald, like aquamarine, belongs to the beryl species, of which there are also other differently colored varieties. The emerald is the most prized of all. The coloring substance is chromium, sometimes vanadium. Its color is very stable to light and heat. It only changes at temperatures of 700/800 degrees. Only the best qualities are transparent. More valuable is the intense green color, which gives the stone a value higher than that of any pale stone, however pure it may be. All stones are very fragile.

The most significant deposits are in Colombia. The most important location is the Muzo mine. Other less important fields are in Brazil, Zimbabwe, Northern Transvaal, Zambia, Russia, Tanzania, Pakistan, Australia, USA.

Sapphire

Color: blue in various shades
Hardness = 9
Composition = Al2 O3 Aluminium dyoxide

The name sapphire is now given to the blue variety of gem quality corundum. Other corundums are red (ruby) and all other colors (green, pink, yellow, blue, etc.). The colorless corundum is called leucozaffiro, the orange one is padparadscia. The coloring elements for sapphire are iron and titanium (the most valuable color is cornflower blue; vanadium for violet corundum; small amounts of iron for green and yellow colors; small amounts of chromium for pink. Inclusions of rutile create silky reflections and if abundant they give the optical effect of chalking (corundum asteria). The various corundum and sapphire are more common than their ruby ​​brother because the coloring elements (particularly iron) are more abundant than chromium, responsible for the red in ruby.

The most important fields from the commercial point of view are in Australia, Burma; Sri Lanka and Thailand. Once upon a time the finest qualities of sapphire came from Kashmir (India). Other deposits are found in Brazil, Cambodia, Kenya, Malawi, Zimbabwe and northern Tanzania

Opal

The opal is usually divided into 3 groups:
noble opal, with its typical play of colors (harlequin)
fire opal, yellow-red
common opal, very widespread.

Physical characteristics:
color: white, gray, blue, green, orange, black; sometimes it has harlequin.
Hardness: 5,5-6,5
Chemical Formula: (SiO2•nH2O),silicon oxide with water.

NOBLE OPAL
The typical feature of this gem is the harlequin, which consists of patches of light that change color as the angle of observation varies. The opal contains a variable percentage of water up to 30%. Since over time the water can evaporate, the opal can fracture and consequently the colors become less iridescent. The preservation of the opal in moist cotton preserves it from aging and enhances the play of colors. Opal is sensitive to pressure, shocks, acids and lye. Also pay attention to the embedding.

Noble opals are divided into 2 groups:
1) white opals: white or light background.
2) black opals: rarer, with dark gray, dark blue, dark green, black gray or black background (very rare)

The noble opal found on the mother rock (boulder opal) is called the opal matrix. Until the end of the nineteenth century, the best quality of noble opal came from the Andenisite lavas of Cervenica, in Czechoslovakia.

Subsequently, Australian deposits were discovered, of which the most famous (Lightning Ridge, White Cliffs, Coober Pedy, Andamooka, Bulla Creek and Burcoo River), in Brazil, Guatemala, Honduras, Japan, Nevada (USA).

The “cabochon” cut enhances the play of colors to the maximum. There are various mystifications: doublets, triplets, dyes, or impregnation with artificial resins. A synthesis of white opal has been produced in France since 1970

FIRE OPAL
It is so called for its characteristic orange color. It rarely has harlequin (even if possible), it has a milky appearance. The excellent pieces are clear and are very sensitive to stress. The most famous deposits are: Mexico (Hidalgo and Queretero), Brazil, Guatemala, Honduras, USA, Western Australia.

COMMON OPAL
Generally opaque it has many commercial names: Agate – opal, hyalite, milky opal, musk opal, prase-opal, chrysopal.