Classifying Gemstones

Classifying Gemstones

gemology

Classifying Gemstones
Classifying Gemstones

Many gemstone names can be related back to ancient times before mineralogy provided a scientific basis for categorization.

Gemstones are identified in modern texts first by their mineralogical classification, then by the name of the mineral variety.

A radical is a group of atoms that act as a single unit.

radical

Classifying minerals

Chemical composition and internal atomic structure are used to classify minerals.

The chemical formulas for marcasite and pyrite are identical, but their interior structures are different.

marcasite
marcasite FeS2 ( Ferrous disulfide )
Pyrite
Pyrite FeS2 ( Ferrous disulfide )

The mineralogical categorization of gems is used to categorize them.

Sulfides

A sulfide mineral is formed when a metal or semimetal combines with sulfur. In sphalerite, zinc is the metal.

Sphalerite
Sphalerite (Zn,Fe)S

Native Elements

Mineral formed from a single chemical element is called native elements. They include metals such as gold and nonmetals such as diamond, which is made up of carbon.

Diamond
Diamond C

Oxides

blue sapphire
Blue Sapphire Al₂O₃

When oxygen alone combines with a metal or semimetal, an oxide mineral is formed. Corundum is aluminum oxide when blue it’s called blue sapphire.

Hydroxides

These minerals contain a hydroxyl ( Hydrogen and Oxygen ) radical combined with metal. In diaspore, aluminum is the metal.

Diaspore
Diaspore AlO(OH) Aluminium hydroxide oxide

Halides

A halide is a halogen element ( chlorine, bromine, fluorine, or iodine ) combined with a metal or semimetal. Fluorite is fluorine and calcium combined.

Fluorite
Fluorite CaF₂ ( Calcium fluoride )

Carbonates

The carbonate radical, carbon, and oxygen combine with a metal or semimetal to form a carbonate. in the case of azurite copper is the metal.

azurite
Azurite C2H2Cu3O8

Phosphates

In the phosphates radical of oxygen and phosphorus is combined with the metal or semimetal. Magnesium and aluminum are the combined medals in lazulite.

lazulite
Lazulite MgAl2

Borates

These minerals contain boron and oxygen. In howlite, boron, oxygen, and silicon combine with calcium and water.

Howlite
Howlite Ca2B5SiO9(OH)5

Sulfates

Sulfur forms a radical with oxygen that combines with a metal or semimetal to form a mineral of the sulfate group, Barite is barium sulfate.

Barite
Barite BaSO4

Silicates

In this group, silica (silica and oxygen) radical combines with various metals or semimetals. Silica also occurs uncombined as quartz, whose purple variety is amethyst.

Amethyst
Amethyst SiO₂

Organics

Amber
Amber

Pearl, shell, and coral are organic compounds with well-defined crystal structures and are classified as minerals. Amber, copal, and jet are amorphous and are not considered minerals.

Chemical formulas

The chemical makeup of a mineral is expressed in its chemical formula. the formula indicates the relative proportions of each chemical element that makes up a single structural unit of the mineral .some minerals grade into each other chemically, and this is also noted in the formula. minor amounts of other elements called trace elements, may also be present in a mineral and influence its color. however, these are not included in the formula.

How gemstones are named?

Black Prince's Ruby
Black Prince’s Ruby

Until relatively recent times, there was no real basis for the classification of gems except color .however color names referred to a number of different stones.
The term “Ruby” was used for many Red Stone that was not the red variety of the mineral corundum, the current definition of Ruby. One such example is the Black Prince’s “Ruby” in the British crown jewels which is actually a spinel. Today, gemstones are named after the mineral from which they are cut, such as topaz. Some older names still persist. these include rubellite and indicolite for colored varieties of tourmaline. Many old names are dropping away as modern science is being applied to gemology. However, a number of gem names that are in use today are trade names, with no scientific or mineralogical connection.

Classifying Gemstones in Precious and Semi-Precious is also most important when trading.

Precious and Semi-Precious.

Today, Precious stones are Sapphires, Rubies, Alexandrite, and Emeralds. These three gems are so-called precious.

Semi-Precious stones are Amethyst, Aquamarine, Citrine, Garnet, Onyx, Opal, Peridot, Tanzanite, and Topaz.

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