Semi Precious Stones

Semi Precious Stones:
Semi Precious Stones are also called Gemstones, and have been prized over the centuries for decorative purposes, in jewelry and for their perceived medicinal value and as lucky charms. They are also valued for their rarity and beauty.

Gemstones are often derived from organic material like rocks and stones, but are also derived from plants and animals. The principle characteristics of naturally occurring gemstones are as follows -

• They are usually hard and durable
• They can, at the same time, be brittle and with weak planes.
• They can be cut and polished.
• They can be transparent and opaque.

Synthetic gems are created in a lab setting by melting minerals, mixing as required and letting the mixture recrystallize at a specific temperature and pressure. Imitation gems, on the other hand, are usually of glass or paste.

It takes some skill and specialist knowledge to identify genuine semi precious stones from synthetic gems and artificial gems. If there are swirly patterns or gas bubbles in the gem, then you're probably looking at an imitation gem. With synthetic gems, the identification process is harder as synthetic gems have the same chemical and structural properties as real semi precious stones, and if there are any manufacturing flaws present, you really need to know what to look for.

To test and identify semi precious stones, gem experts or gemologists observe the way the light passes through the gem using special testing equipment. The scratching and streaking tests usually used to identity minerals are not used in testing semi precious stones – you could end up ruining the stones.

Value of Semi Precious Stones:
Previously there was a rigid distinction between precious and semi precious stones by market appeal mainly, but this no longer applies. All kind of gems are used in making jewelry and other items these days. Still, the precious gems like diamonds, rubies, sapphires and emeralds hold a considerable psychological sway.

A value of a semi precious stone depends upon -

• Its rarity. The rarer the stone is, the more its value. For example, gems like Amethyst and Citrine are extremely rare in nature.
• Its hardness. Jade for example is very hard and, as it is not prone to breaking easily, it is extremely suitable for carving. Emeralds and Diamonds on the other hand have to be cut with extreme care and in a limited way, as the former are brittle and the latter can have weak planes.
• Its color. The color of a semi precious stone depends on the way white light passes through it. White light is made up of many different colors of different wavelengths, and as it passes through a gemstone, generally some of these differing color wavelengths are blocked by trace impurities or structure irregularities in the stone or by certain compositional elements that make up the mineral. The color wavelengths that get through are the ones that give the stone its distinctive color/colors. If the white light is filtered through regularly-spaced interferences, the crystal displays an iridescence, as in opals. If the color wave lengths separate and disperse when passing through the crystal, you can see glints of different colors, something seen in a diamond. If the color wave lengths are filtered differently through different crystal axes, you get an effect called pleochroism, where the color will change in intensity according to the angle from which you are viewing the semi precious stone.
• Any special effects caused by impurities and inclusions, like cat's eye and star effects.

Cutting Semi Precious Stones:
While some semi precious stones are used in their naturally occurring form for decoration and various other purposes, most gems undergo cutting and polishing to bring out their beauty and to fit into design settings.

Originally semi precious stones were simply decorated with the name inscriptions of their owners. Later it became fashionable to polish the cleavage planes and crystal faces of the gemstones. This was followed by a cutting style called Cabochon, where the gems were cut into oval or circular shapes with a dome-like surface. The Facet cut method was probably developed in the 15th century or thereabouts. Both these cuts are popular in modern times. Cabochon cuts are mainly done on opaque semi precious stones. Facet cuts are done on transparent gemstones to bring out their luster and quality of light better. It takes a great deal of competency and patience to cut gemstones. The cutter must consider each stone on its own merit, keeping in mind any structural weaknesses and making every effort to highlight its special qualities.

Groups of Semi Precious Stones:

• Beryl
• Chrysoberyl
• Corundum
• Feldspar
• Garnet
• Organic Gems
• Quartz

List of some semi precious stones:

• Agate
• Alexandrite
• Almandine
• Amazonite
• Amber
• Amethyst
• Aquamarine
• Bloodstone
• Carnelian
• Chalcedony
• Chrysoberyl
• Citrine
• Coral
• Cymophane
• Demantoid
• Golden Beryl
• Hematite
• Hessonite
• Jasper
• Labradorite
• Lapis Lazuli
• Malachite
• Moonstone
• Morganite
• Obsidian
• Onyx
• Opal
• Pearl
• Prase
• Pyrope
• Serpentine
• Spinel
• Topaz
• Tourmaline
• Turquoise
• Zircon