Precious Stones: The Four Most Precious Gemstones

Precious Stones: The Four Most Gemstones
Precious Stones: The Four Most Gemstones

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:


Diamonds are the most famous and beloved gemstone, prized for their beauty, rarity, and durability. They are the hardest natural substance on Earth, composed almost entirely of carbon atoms arranged in a specific crystal structure. This atomic arrangement is what gives diamonds their brilliance and fire.

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. 

Diamonds come in a variety of colors, although colorless diamonds are the most common and most valuable. Other colors include yellow, brown, pink, blue, green, and even black. The color of a diamond is caused by the presence of trace elements or structural defects within the crystal lattice.

Diamonds are not only beautiful gemstones but also have important industrial applications. Their extreme hardness makes them ideal for cutting tools, grinding wheels, and drill bits. They are also used in a variety of electronic applications due to their excellent thermal conductivity and electrical insulating properties.

Key properties of diamonds:

  • Hardness: 10 on the Mohs scale (the hardest natural substance)
  • Refractive Index: 2.418 (at 500 nm)
  • Luster: Adamantine (brilliant)
  • Crystal System: Cubic
  • Chemical Composition: C (carbon)


Emeralds are a vibrantly green gemstone variety of the mineral beryl. Their rich green color has been admired for centuries and is often associated with royalty, wealth, and spring. Emeralds are known for their beauty, but they are also quite rare and valuable.

Emeralds are formed when beryllium, chromium, and vanadium combine under high pressure and temperature within hydrothermal veins or metamorphic rocks. These conditions are rare, and the presence of chromium is what gives emeralds their characteristic green color. Trace amounts of vanadium can also contribute to the green color and may influence the specific hue.

Emeralds range in color from deep bluish green to a lighter yellowish green. 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.

Emeralds are popular gemstones for jewelry, particularly in engagement rings, pendants, and earrings.

Key properties of emeralds:

  • Hardness: 7.5 - 8 on the Mohs scale (moderately hard)
  • Refractive Index: 1.56 - 1.59
  • Luster: Vitreous (glassy)
  • Crystal System: Hexagonal
  • Chemical Composition: Be₃Al₂SiO₆ (beryllium aluminum silicate) with trace amounts of chromium and vanadium

May Birthstone: Emerald


Rubies are stunning gemstones, prized for their fiery red color and exceptional brilliance. They are a variety of the mineral corundum, the same mineral that forms sapphires. Only red corundum is entitled to be called ruby, all other colors being classified as sapphires. This captivating red color comes from the presence of the trace element chromium within the corundum crystal structure.

Rubies range in color from a deep pinkish red to a vibrant pigeon blood red. The most valuable rubies have a saturated red color with a hint of blue, known as pigeon blood red. This captivating red color comes from the presence of the trace element chromium within the corundum crystal structure.

Rubies are popular gemstones for a variety of jewelry pieces, including engagement rings, pendants, necklaces, and earrings. High-quality rubies can be extremely valuable, fetching even higher prices per carat than diamonds. The value depends on factors like color, clarity, cut, and carat weight.

Key properties of a ruby:

  • Hardness: 9 on the Mohs scale 
  • Refractive Index: 1.760 to 1.766
  • Luster: Adamantine
  • Crystal System: Trigonal
  • Chemical Composition: Al₂O₃ (Aluminum Oxide)


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.

Key Properties of sapphires:

  • Hardness: 9 on Mohs scale
  • Refractive Index: 1.760 to 1.769
  • Luster: Adamantine
  • Crystal System: Trigonal
  • Chemical Composition: Al₂O₃ (Aluminum Oxide) with trace elements causing color variations.

Beyond the Big Four

It's important to note that the distinction between precious and semi-precious stones is not a scientific classification. Many semi-precious stones, like opals and alexandrites, can be just as valuable and rare as some precious stones. Ultimately, the value and desirability of a gemstone depend on a combination of factors, including its rarity, color, clarity, cut, and size.

Whether you're drawn to the timeless elegance of a diamond, the fiery allure of a ruby, the captivating blue of a sapphire, or the verdant beauty of an emerald, the world of precious stones offers something for every taste. These natural wonders have captivated hearts for centuries and continue to be a source of fascination and desire.

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