[Jewelry making - Article 00130] - [Orchid] How minerals and gemstones are formed

[Sandra I. Smith]

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    Do you know what diamonds, rubies, and emeralds are? "Jewels" is the
    answer most people offer. It's an accurate answer, but it doesn't
    tell the fascinating story behind these treasures from nature. 

    Jewels are the end result of a process begun billions of years ago
    when the Earth was first formed. All that existed originally were
    the elements. Common elements you may be familiar with include
    oxygen, silicon, and carbon. Gold and silver are also elements. Far
    below the Earth's surface, where they were subjected to tremendous
    heat and pressure, certain elements combined to form minerals. 

    Atoms of an element may combine with other atoms of the same
    element; or they may combine with atoms from other elements to make
    compounds. Sulfur is a pure mineral, that is, it contains only
    sulfur atoms. Sulphur atoms may also combine with iron atoms to form
    a compound mineral called pyrite. 


    Minerals, and substances made from them, all belong to the mineral
    kingdom, which includes more than 3000 members. Approximately 100
    minerals are classified as gemstones. Although a few gemstones are
    used for industrial purposes, most have value solely to collectors.
    Only about a dozen gemstones are suitable for use in jewelry. 

    Due to the exquisite way in which most gemstones crystallize, they
    were described as "the flowers of the kingdom" by Abbe Hauy, an
    early French crystallographer. 

    Diamond, which is pure carbon, is the only gemstone formed from one
    element. All the other minerals that we classify as gemstones are
    compounds--they are minerals that include atoms from more than one
    element. 

    Minerals formed from more than one element are also called
    chemicals. Like other minerals, gemstones can be described by
    chemical formulas. For example, quartz is a combination of silicon
    and oxygen called silicon dioxide. 

    A gemstone's chemical composition determines its appearance.
    Although they are both blue stones, sapphire and turquoise look and
    feel entirely different. That's because sapphire is an aluminum
    oxide (aluminum and oxygen) with a trace of titanium, while
    turquoise consists of aluminum, phosphate, and copper. 

    Another important factor affecting the appearance of gemstones is
    the way in which the atoms are bonded together within the stone.
    Diamond and graphite both are pure carbon and have identical
    chemical formulas. However, they are entirely different substances
    due to the way the carbon atoms in each fit together. Carbon atoms
    in a diamond crystallize in a tightly-bonded regular pattern. The
    same atoms in graphite form scales or irregular masses, which makes
    it soft and slippery. 

    Three criteria distinguish the flowers of the kingdom from other
    minerals: their beauty, rarity, and durability. 

    Beauty in gemstones, like everything else, is a matter of personal
    taste and changing fashions. The beauty in some gems, like
    turquoise, is based on color alone. In others, the color is
    secondary to the brilliance, or "fire," such as with diamonds, the
    most prized of which are colorless. A variety of colors in one
    stone, such as the green stripes in malachite, appeal to many. 

    Gemstones that are hard to find are valued more highly than those
    that are abundant. Treasured for its changeable colors, alexandrite
    is also valuable because it is so rare. Very little natural
    alexandrite exists. Other gemstones, although seemingly abundant,
    yield only a few specimens that are of usable quality. Gem-quality
    opals are difficult to find and very expensive. Common opal is
    abundant and inexpensive. Many rare and beautiful gemstones can't be
    used in jewelry because they aren't durable. They disintegrate or
    break too easily. To be durable, a stone must be stable, tough, and
    hard. 

    Stable gemstones remain unchanged by heat, light, or chemicals. For
    example, strong light can cause yellow topaz to fade. Toughness
    refers to the brittleness of a gemstone. The more brittle it is, the
    easier it will break. Jadeite and nephrite (the two jades) are the
    toughest, or most difficult, to break. Hardness, which is different
    from toughness, is the ability of a gemstone to resist scratching
    and general wear. Diamonds are the hardest of all gemstones. 

    Gemstones usually go to a lapidary after they are mined. The
    lapidary does the final cleaning, which may involve grinding off the
    matrix, or rock, in which the gemstone was buried. While some
    gemstones may be simply polished, most are cut. The softer ones,
    like turquoise, are usually cut in rounded shapes called cabochons.
    Cabochons were the only way in which stones were cut until about the
    14th century, when faceting was developed. 


    Only the harder gemstones can be successfully faceted. Faceting is
    the process of cutting a gemstone to improve its beauty by making it
    reflect more light. A faceted stone has had all rounded and uneven
    surfaces cut into flat "faces," which are highly reflective. A
    gemstone that has been cut and polished is called a gem, or jewel. 

    People who study gemstones and gems are called gemologists. Gemology
    is a relatively new field that began as a speciality of mineralogy.
    Gemologists must understand mineralogy, crystallography, physics,
    chemistry, and geology. As more synthetic, enhanced, and imitation
    gems become available, gemologists must also acquire the knowledge
    and equipment necessary to distinguish fake from real. 

    The flowers of the kingdom have captivated people since prehistoric
    humans first picked up shiny stones from ancient streambeds. These
    dazzling treasures from nature, eons in the making, are today
    crafted into jewelry of timeless beauty. 


****Sandra I. Smith, Writer ****




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