Common terms

• Inclusions, an inclusion within a gem stone can be an included crystal, cloud, feather, fracture, etc... Inclusions are different from blemishes, which are imperfections at the surface of the gem stone. Inclusions are not always bad. Inclusions can be used like a finger print, to identify valuable gem stones. Inclusions can be used to tell between natural and synthetic gem stones, and in some types of gem stones, the inclusion can even pinpoint the source of the natural stone. In some cases, inclusions can actually increase the brilliance of a gem stone. Beware of a emerald and ruby which do not contain inclusions, as these are extremely rare, and are probably synthetic.
  
  
• Blemish, a defect in a gem stone found at the surface, such as a pit, nick, scratch, chip or even an extra facet where none should be. A blemish differs from an inclusion, which is internal to the gem stone.
  
  
• Calibrated, a gem stone whose dimensions are a standard (mm) size, and are cut to fit ready made jewelry pieces.
  
  
• Carat (ct.), unit of weight. 1 carat is equivalent to 0.2 grams. Carat weight should not be confused with the term karat (kt.), which is used to measure the quality of gold, nor carrot which refers to a plant. The abbreviation (cwt.) is used to indicate the total weight of two or more gem stones, such as the weight of a parcel of stones, or a pair of stones often traded as a group. Carat weight should not be used to judge the size of a stone, as differences in cutting and the depth of a stone can allow stones of the same weight to have different dimensions. Also, the density, or specific gravity of different materials can have the same effect. A one carat sapphire for instance is much smaller than a one carat opal. When looking for a setting for a particular gemstone, the stones dimensions in millimeters should be used, not the carat weight.
  
  
• Cut, different types of stones have different specific gravity and hardness, and subsequently different critical angles are necessary to achieve the maximum brilliance of the cut gemstone. Different shapes are round brilliant, square, emerald cut, oval, marquis, cushion, and heart shape to name a few. 
  
  
• Gram, unit of weight in the Metric system. 1 ounce (avdp.) is equivalent to 28.349523 grams (141.747615 ct.). Rough (uncut) material is often sold by the gram, whereas cut or finished gemstones are generally sold by the carat.
  
  
• Karat (K or Kt.), a measure of the amount of gold present in a gold alloy, expressed in 1/24ths. Under 10 Kt. gold is not legally called gold in the U.S. (9 Kt. in England.) The number in parentheses in the table below indicates a marking that is found on some foreign manufactured jewelry, expressed in thousandths.
  
  • 10 kt. is 10/24 or 41.60% gold (416).
  • 12 kt. is 12/24 or 50.00% gold (500).
  • 14 kt. is 14/24 or 58.33% gold (585).
  • 18 kt. is 18/24 or 75.00% gold (750).
  • 24 kt. is 24/24 or 100% "solid" gold (usually 99.999%).
    
    
• Kilogram (kg.), a unit of weight equivalent to 1000 grams, or 2.2046226 pounds (avoirdupois), or 32.150737 troy ounces.
  
  
• Melee, also known as an accent stone, a small round gemstone, usually less than 4mm in diameter. Melee stones are placed around a larger center gemstone to accent it, and make the center stone or jewelry piece appear larger.
  
  
• Millimeter (mm.), a measure of distance in the Metric system. 1 inch is defined as 25.4 millimeters. The metric system is the standard used in the jewelry industry, by gemologists, and by science worldwide.
  
  
• Point, unit of weight. 1 point is equivalent to 0.01 (1/100) carats. The term point should not be confused with the number of facets that a gem stone may have.