Precious Gem Stones Chantaburi Thailand

Jewelry Shopper's Checklist

Once you're ready to buy jewelry, shop around. Compare quality, price and service. If you're not familiar with jewelers in your area, ask family members, friends and co-workers for recommendations. Also, when ordering online and you've never heard of the seller, check on its reputation with the Better Business Bureau or the state attorney general's office. You also should:

• Ask for the store's refund and return policy before you buy. When ordering online, keep printouts of the web pages with details about the transaction, including refund and return policies in case you're not satisfied.
  
  
• Check for the appropriate markings on gold jewelry.
  
  
• Ask whether a gemstone is natural, laboratory-created, or imitation.
  
  
• Ask if the gemstone has been treated. Is the change permanent? Is special care required?
  
  
• Make sure the jeweler writes on the sales receipt any information you rely on when you make your purchase, such as the gemstone's weight or size. Some jewelers also may supply a grading report from a gemological laboratory.

What is a Gemstone?

Gemstone is a collective term for all objects used with ornamental stones for personal adornment that possesses beauty, durability, and stability. Beauty, a quality that varies among individuals, can be based on one or any combination of: color or lack of color, luster, transparency, or enhanced optical properties due to cutting and fashioning by the lapidary. Durability is the resistance of the gemstone damage and dependent upon physical properties, such as hardness and tenacity. Tenacity is the resistance to bending and breaking, while hardness measures the resistance to scratch. Diamond cannot be scratched by any other mineral and therefore, it is a gem with high hardness; diamond has low tenacity, in part due to perfect cleavage. Nephrite jade is relatively soft for a gem, easily scratched by dust in the air, but it is composed of fibrous crystals that resist breaking and therefore, it is tough or has high tenacity. Stability refers to the gem's ability to retain color inspite of heat, light, or chemical assaults.

Of the 4,000+ known minerals, 70 possess qualifications for gemstones, but of these, only approximately 20 are commonly encountered (Hurlbut & Kammerling, 1991, p. 3). These minerals include: diamond, corundum (ruby, sapphire, star ruby and sapphire), beryl (emerald, aquamarine, morganite, goshenite, golden or heliodor), chrysoberyl (cat's eye & alexandrite), spinel, topaz, zircon, tourmaline (indicolite, rubellite, schorl, elbaite), garnet group (almandite/almandine, rhodolite, pyrope, grossular/tsavorite, spessartine, uvarovite), quartz: crystalline (rock crystal, amethyst, citrine, cairngorm or smoky, rose, aventurine, tiger's-eye, rutilated), quartz: cryptocrystalline (chrysoprase, carnelian, sard, bloodstone, agate, onyx, jasper, agatized or petrified wood), olivine peridot (chrysolite), jadeite jade, tremolite-actinolite or nephrite jade, spodumene (kunzite, hiddenite), feldspar group (microcline amazonite, labradorite, orthoclase moonstone, oligoclase sunstone), turquoise, lapis-lazuli, and opal.

THE COLORS OF GEMSTONES

The most common cause of color in gemstones is the presence of a small amount of a transition metal ion. These transition metal ions have an incomplete set of 3d electrons. Changes in the energy of these electrons correspond to the energy of visible light. When white light passes through a colored gemstone or is reflected by it, some of the energy of the visible light is absorbed, causing 3d electrons in the transition metal ion to undergo an energy change. The light that is transmitted or reflected appears colored, because those colors corresponding to 3d-electron energy transitions have been absorbed. The table lists several common gemstones, their chemical compositions, colors, and the origins of these colors.

Gem	Formula	Color	Origin Of Color
Ruby	Al2O3	Red	Cr3+ replacing Al3+ in octahedral sites
Emerald	Be3Al2(SiO3)6	Green	Cr3+ replacing Al3+ in octahedral site
Alexandrite	Al2BeO4	Red/Green	Cr3+ replacing Al3+ in octahedral site
Garnet	Mg3Al2(SiO4)3	Red	Fe2+ replacing Mg2+ in 8-coordinate site
Peridot	Mg2SiO4	Yellow-green	Fe2+ replacing Mg2+ in 6-coordinate site
Tourmaline	Na3Li3Al6(BO3)3(SiO3)6F4	Pink	Mn2+ replacing Li+ and Al3+ in octahedral site
Turquoise	Al6(PO4)4(OH)8A4H2O	Blue-green	Cu2+ coordinated to 4 OHG and 2 H2O
Sapphire	Al2O3	Blue	Intervalence transition between Fe2+ and Ti4+ replacing Al3+ in adjacent octahedral sites
Aquamarine	Be3Al2(SiO3)6	Blue	Intervalence transition between Fe2+ and Fe3+ replacing Al3+ in adjacent octahedral sites
Diamond	C	Colorless pale blue or yellow Color	centers from nitrogen atoms trapped in crystal