What Are the Four Most Precious Stones?

Gemstones which are highly valuable for their hardness and rarity, are known as Precious Stones. Precious Stones are generally expensive in comparison of Semi-Precious Stones. There are only four Precious Stones:

Diamond

Diamond is renowned for its superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. In particular, it has the highest hardness and thermal conductivity of any bulk material. Most natural diamonds have ages between 1 billion and 3.5 billion years. Most were formed at depths of 150 to 250 kilometers (93 to 155 mi) in the Earth's mantle, although a few have come from as deep as 800 kilometers (500 mi). Marketing has significantly affected the image of diamond as a valuable commodity.

However, many people expect a diamond to be unbreakable. This is not true. A diamond's crystal structure has ‘hard’ and ‘soft’ directions. A blow of sufficient force, in an exact direction, can crack, chip, split or even shatter a diamond. The Crater of Diamonds State Park in Arkansas is the world’s only diamond mine open to the public and this is a dig-for-fee operation for tourists and rock enthusiasts. An average of 74,000 visitors comes to the park each year. About one out of 100 visitors find a diamond.

Emerald

Emerald is one of the most fascinating and beautiful gemstones. Emerald is a precious gemstone and a variety of the mineral beryl colored green by trace amounts of chromium and sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. The crystals are usually small with average length of 2 - 5 cm and width of 1 - 1.5 cm. Larger crystals are usually semitransparent to opaque.

The most desirable color is a slightly bluish green in a medium dark tone with strong to vivid saturation. Clarity is important, but inclusions are tolerated more in this variety than virtually any other gem. Top quality, unenhanced stones (with certification) can bring as much as 50% more in price than treated stones of the same size, color, and clarity.

Ruby

Ruby is the red variety of the mineral corundum, one of the hardest minerals on Earth, of which the sapphire is also a variety. Corundum is the mineral form of alumina which crystallizes in the hexagonal system. The red color of ruby results from a small admixture of chromic oxide. Only red corundum is entitled to be called ruby, all other colors being classified as sapphires. The most prized tint is blood red or crimson known in the trade as 'pigeon's blood' red.

The quality of a ruby is determined by its color, cut, and clarity, which, along with carat weight, affect its value. The brightest and most valuable shade of red called blood-red or pigeon blood, commands a large premium over other rubies of similar quality.

Sapphire

Sapphire is also a variety of the mineral Corundum and represents all the colors except red Corundum, which is Ruby. Its physical and chemical properties are virtually similar to properties of Ruby. Blue is the main color of the Sapphire whereas this gemstone is also found in colors like green, orange, pink, gray, colorless, black, brown, and purple. The word 'Sapphire' in its plain context refers only to blue Sapphire, unless a prefix color is specified. Sapphire with a color other than blue is often called a 'Fancy' in the gem trade. The Sapphire gemstone symbolizes harmony, friendship and loyalty.

Sapphire is the most precious blue gemstone. It is a most desirable gem due to its color, hardness, durability, and luster. Value of this gemstone depends on its size, color and transparency. Top-quality sapphires are extremely rare in all the gemstone mines of the world. Cutting of this gemstone requires great skills and experience and it is the job of the cutter to orientate the raw crystals in such a way that the color is brought out to its best improvement.