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Gemstone

A gemstone or gem (also called a fine gem, jewel, or a precious or semi-precious stone) is a piece of mineral crystal, which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli) or organic materials that are not minerals (such as amber or jet), are also used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone. Apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter; a diamond worker is a diamantaire.

Characteristics and classification

 

A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. The biggest pebble here is 40 mm long (1.6 inches).

The traditional classification in the West, which goes back to the Ancient Greeks, begins with a distinction between precious and semi-precious; similar distinctions are made in other cultures. In modern usage the precious stones are diamond, ruby, sapphire and emerald, with all other gemstones being semi-precious. This distinction reflects the rarity of the respective stones in ancient times, as well as their quality: all are translucent with fine color in their purest forms, except for the colorless diamond, and very hard, with hardnesses of 8 to 10 on the Mohs scale. Other stones are classified by their color, translucency and hardness. The traditional distinction does not necessarily reflect modern values, for example, while garnets are relatively inexpensive, a green garnet called tsavorite can be far more valuable than a mid-quality emerald. Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone. Use of the terms 'precious' and 'semi-precious' in a commercial context is, arguably, misleading in that it deceptively implies certain stones are intrinsically more valuable than others, which is not the case.

In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition. For example, diamonds are made of carbon (C) and rubies of aluminium oxide (Al
2O
3). Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in. For example, diamonds, which have a cubic crystal system, are often found as octahedrons.

Gemstones are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the Emerald (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow), and morganite (pink), which are all varieties of the mineral species beryl.

Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and luster. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.

Material or flaws within a stone may be present as inclusions.

Gemstones may also be classified in terms of their "water". This is a recognized grading of the gem's luster and/or transparency and/or "brilliance". Very transparent gems are considered "first water", while "second" or "third water" gems are those of a lesser transparency.

Gems and planets

Ruby for Surya (Sun),

Pearl for Chandra (Moon),

Red Coral for Mangala (Mars),

Emerald for Budha (Mercury),

Yellow sapphire for B?haspati (Jupiter),

Diamond for Shukra (Venus),

Blue sapphire for Shani (Saturn),

Hessonite for Rahu (the ascending node of the Moon)

Cat's Eye for Ketu (the descending node of the Moon),

List of gemstones

A number of gemstones have gained fame, either because of their size and beauty or because of the people who owned or wore them. A list of famous gemstones follows.

Contents

1 Alexandrites

2 Aquamarines

3 Diamonds

4 Opals

5 Pearl

6 Ruby

7 Sapphires

8 Spinels

9 Topaz

Alexandrites

  • Smithsonian museums' Alexandrite, the largest cut alexandrite weighing 65.08 carats.

Aquamarines

A birthstone.

  • The Dom Pedro - The world's largest cut and polished aquamarine. Housed in the permanent collection of the Houston Museum of Natural Science

Diamonds

See List of famous diamonds given bellow

Opals

  • The Andamooka Opal, presented to Queen Elizabeth II, also known as the Queen's Opal
  • The Aurora Australis Opal, considered to be the most valuable black opal
  • The Black Prince Opal, originally known as Harlequin Prince
  • The Empress of Australia Opal
  • The Fire Queen Opal
  • The Flame Queen Opal
  • The Flamingo Opal
  • The Halley's Comet Opal, the world's largest uncut black opal
  • The Jupiter Five Opal
  • The Olympic Australis Opal, reported to be the largest and most valuable gem opal ever found
  • The Pride of Australia Opal, also known as the Red Emperor Opal
  • The Red Admiral Opal, also known as the Butterfly Stone

Pearl

  • Arco Valley Pearl
  • La Peregrina
  • Satlada – A seven-stringed pearl necklace of the Nizams. Most pearls are white but can be other colors as well.
  • The Pearl of Lao Tzu - Philippines

Ruby

  • The DeLong Star Ruby
  • The Hixon Ruby Crystal
  • The Midnight Star Ruby
  • The Neelanjali Ruby
  • The Rajaratna Ruby
  • The Rosser Reeves Ruby

Sapphires

  • The Logan sapphire
  • The Queen Marie of Romania Sapphire
  • The Ruspoli Sapphire
  • The Star of Asia Star Sapphire
  • The Star of Bombay, given to Mary Pickford by Douglas Fairbanks, Sr
  • The Star of India
  • The Stuart Sapphire
  • The Black Star of Queensland, with a weight of 733 carats (146.6 g) The largest star sapphire in the world.

Spinels

  • The Black Prince's Ruby, actually a spinel mounted on the Imperial State Crown
  • The Samarian Spinel, the world's largest spinel
  • The Timur Ruby, believed to be a ruby until 1851, hence its name

Topaz

  • The American Golden Topaz, the largest cut yellow topaz, weighing nearly 23000 carats (4.6 kg).
  • The Chalmers Topaz, a 5,899.5-carat (1.17990 kg) cut topaz.