It is not possible to determine the time when people decided that some stones are of great value, and some have practically no value. Even primitive people had amulets made of various stones, which, according to beliefs, protected from troubles and diseases, brought good luck on the hunt. In the Bible (Old Testament) you can find a description of the body plate of the minister of the temple of Aaron, which had 12 precious stones as decoration.
What stones are precious?
So, the number of precious stones includes only the following minerals - natural diamonds, rubies, sapphires, emeralds, alexandrites. This list includes still processed or raw natural pearls. Amber of a unique type is also equated with precious stones. There are no other precious stones.
Why are some stones considered precious?
To begin with, it should be noted that in the distant past, precious stones (gems) differed exclusively in color. If the stone had a red color, then it was automatically considered a ruby, all blue stones were credited to the sapphire category, and green ones were emeralds.
Rubies, sapphires and emeralds.
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The very value of the stones was determined by two important factors - the beauty and rarity of the mineral. Even the most beautiful stone will not be precious if it is found in every quarry like a cobblestone. Such a stone can become ornamental maximum. On the other hand, even a rare stone that does not have beauty is unlikely to arouse particular interest in anyone other than scholars. And in this category, money is rare, so the stone cannot become precious. After all, the value of any thing is determined by the price that the buyer is willing to pay. And also labor costs for the extraction of natural material are included in the price on a full machine.
Properties of precious stones
After people drew attention to the beauty and rarity of minerals, which began to be called precious stones, they began to study the properties more specifically. It turned out that gems are distinguished by enviable durability and great strength. Most stones are destroyed over time by water and wind; precious stones can last hundreds of thousands of years unchanged.
Diamond.
Diamonds are considered the most expensive stones not only because of their rarity and beauty (after cutting), but also because of their own exceptional strength. It is the hardest material in nature, and for a long time a diamond could only be scratched with another similar stone. Only in the 20th century, materials were created synthetically superior to diamonds in hardness.
Composition of precious stones
Although gemstones have a number of properties in common, they are completely different minerals.
Diamond
According to the chemical formula, diamond is the simplest. It is nothing more than carbon in its purest form, the closest relative of diamond is graphite, which serves as the core of drawing pencils. True, diamonds are formed at tremendous temperatures and pressures.
Sapphire
Sapphires are a type of corundum, chemical formula Al2O3, that is, it is aluminum oxide. The usual blue color is due to impurities in the base matrix of iron and titanium.
Ruby
Ruby is also a type of corundum whose chemical formula is the same as sapphire. The difference in the color of the minerals is due to the difference in impurities. The red color of ruby is provided by the presence of chromium in it in small quantities. In medieval Russia, sapphires and rubies were called with one word yakhont.
Emerald
Emerald belongs to the minerals of the beryl group and has a complex chemical formula Be3Al2Si6O18. Its grassy green color is due to chromium oxide or vanadium oxide. Sometimes, in addition to these impurities, emeralds contain a small amount of iron oxide.
Alexandrite
Alexandrite, like emerald, belongs to the beryl, or rather chrysoberyl group. Therefore, the first alexandrite was found in the emerald deposits of the Urals. The chemical formula of alexandrite is BeAl2O4. The mineral has an interesting property of changing color depending on the lighting. In daylight, alexandrite has various shades of green, and in artificial light, it acquires all sorts of shades of red.
