What is a gemstone - properties of gemstones

Properties of the stone material - physical and chemical properties

A gemstone can be a mineral, that is a crystaline piece where the whole piece have the same basic chemical composition in its crystal lattice. It can also also be a rock art. A rock art contains crystals of different types of lattice composition. In some rare instances also amorphous or glassy substances are used as gemstones. An example is the glassy substanses Opal and Obsidian, and the amorphous substance Ember.

The tern "gemstone" does not have any clear definition. Neither has the term "jewel" used about precious gemstone any clear definition. Here are listed some properties that can make a stone to a gemstone.

Beauty: A gemstone must be beautiful. But beauty consists of several sub-properties. In the following these are listed.

Colour beauty: A pleasant colour is a requirement for a gemstone. A clean clearness as for example in a perfect rock crystal or a clean blackness as for example in a black onyx is also special instances of colour beauty. Either the stone must have a uniform clean colour, or nice shadings of different colours. The colour can be a property of the stone material. It can originate from dissolved chemicals or atoms in the crystal lattice. It can originate from refraction of light within the crystal, as for example in a clear diamant. It can also have its origine in microscopic inclusion of other minerals in a crystal.

Colour play or dispersion: The colour of a stone should not be dead or inert. It should sift somewhat and show to be alive according to the type and strength of light falling upon the stone, and according to the angle of the light. Colour play has its oriogin in light refraction in the whole stone or in layers within the stone. Flourescence may also contribute to a beautiful colour play, but can also sometimes destroy the beauty of a stone. Fluorence is the ability to send back light of another colour than that sent into the stone. Colour play depend very much upon the way a gemstone is cut. For example is a diamond cut to maximize the colour play.

Light play or Brilliance: This is internal or external reflexes from a stone that changes all the time as the angle of light upon the stone or the angle of seeing the stone from are changed. The brilliance can look like thousands of sparcles emanating form the stone all the time. Light play depend very much upon the way a gemstone is cut. For example is a diamond cut to maximize the brilliance.

Purity: A gemstone must be free from ugly inclusions or spots of foreign elements that do not add to the beauty of the stone. It must also be free from dissolved substances that shades for the colour or colour play. An area with many small inclusions of impurities in a stone is often called a cloud. However, inclusions or spots can somentimes also increase the beauty of the stone, for example if the inclusions have fine colours, add colour play or reflect light to increase the brilliance.

Claearness: Clearness is the degree with which a stone is distorting an image seen through the stone. Clearness can be a quality that makes a stone into a gemstone. However, if a stone is unclear in such a way that seeing through the stone gives the impression of a nicely coloured or shaded mist, also this can make a stone to a gemstone.

Robustness: In order to be used as a gemstone, the piece must be enough robust against mechanical impacts, chemical ingredients, temperature or other physical infuences. Robustness consist of several sub-properties:

Hardness: Hardness is a measure of the strongest force a stone can withhold without bursting, and is perhaps the most important property that makes a stone robust. Hardness is measured with a logaritmic scale from 0-10. That means in fact that a stone of hardness 7 is 10 times harder than a stone of hardness 6. Diamonds are one of the hardest substances found, with the hardness of 10 on the scale.

Rareness: A beautyful stone is liker to be regarded as a gemstone if it is rare. Looking at something rare that gives you another experience than all the usual things sou see around you, stimulate the senses and feelings more that looking at any familiar object. However, a stone need not be extremely rare to give this kind of experience.

Symmetry: The colour play, brilliance, clearity or other properties should usually be uniform througout the stone, or show a symmetry according to an axis or point.


Properties related to the way the stone has been crafted

Here are listed some other properties that are used to characterize agemtsones, and especially diamonds.

Crown: This is the top part of the diamond above the girdle.

Cut: Cut refers to the arrangement of a diamond's facets. A diamond which is "ideal cut" captures and reflects back from the interior of the stone the maximum play of light. This is not the same as the shape of a diamond.

Cutlet: This is the bottom facet of a diamond, usually very small. If itoo large, when you look it will look like the diamond has a hole in the middle, straight down through the table.

Eye-Clean: Refers to a diamond that has no inclusions or blemishes visible to the naked eye.

Facet: A polished surface on a diamond. A round, full-cut diamond usually has 58 facets, 33 on the crown and 25 on the pavilion.

Fire: Rainbow colors resulting from the dispersion of light.

Flawless: Diamond without external or internal blemishes or inclusions seen under 10X magnification are calld flawless.

Fluorescence: A diamond will absorbe energy from ultraviolet (UV) light, causing the stone to glow this energy out egain as visible light in various colors.

Full-Cut: A diamond with 58 or more facets.

Gemologist: A person who has been trained and certified in diamonds and colored stones.

Girdle: This is the circumference of a diamond which is usually held by prongs of a setting and separates the crown and pavilion. The purpose of the girdle is to protect the edge of the stone from chipping.

Head: The prongs which hold a diamond in its setting.

Karat: This is another thing than carat-weight of a diamond. This is the measure of the purity of gold; 24-karat being pure gold. Jewelry is made from 18K and 14K gold, and contains other metals for strength.

Laser-Drilled: Treated with a laser to remove carbon spots.

Light Return: The light that is returned from the diamond and not leaked through the pavilion (bottom) of the diamond.

Loupe: A small magnifying glass used to view gemstones.

Off-Make: An ill-proportioned diamond.

Pavé: A method of setting diamonds very closely together, giving the illusion of one or more larger diamonds.

Pavilion: The bottom part of the diamond below the girdle. It has an ideal angle of 40.75 degrees. The pavillion acts as a very highly polished and precise mirror that throws the light back through the other facets.

Point: One-hundredth of a carat.

Refraction: Refraction refers to the bending and slowing of light passing at an oblique angle from the medium of one optical density (such as air) into a medium of greater optical density (such as a diamond). The refraction on passing of the light from air into the diamond and from the diamond back into the air creates the fire of a diamond, because the various colors of the white light are refracted to various degrees and thus separated from each other.

Semi-Mount: A setting which is complete except for the main stone, which will be selected separately.

Shape: This is not the same as cut, shape means the geometric for of the stone. Popular shapes include the round brilliant, marquise, emerald cut, pear and oval.

Single-Cut: A diamond with only 16 or 17 facets.

Sparkle: Flashing effect produced when a diamond is moved in the light.

Symmetry: The symmetry is the quality of efficient light reflection and return. It is a function of proper attention to cutting angles.

Table: This is the largest and most important facet in a diamond situated at the top.

Tiffany: A simple, elegant 2-3 mm ring setting with a head with prongs that holds a single diamond.

Transparency and opaqueness: A stone that let through all the light that comes onto it, is totally transparant. If no light is let through, the stone is opaque.