A carat is a type of measurement used to describe the mass or weight of a gem. The term was initially applied to diamonds only. Now it applies to most precious and semi-precious stones.
Some confusion exists in the very word carat, since gold is also evaluated in carats or Karats. Karat is the more traditional spelling when referring to gold and does not apply to mass. Instead, gold is classed by purity. Twenty-four Karat gold, for example, has the greatest purity, while 10 Karat gold has the least.
When the term carat refers to a gem’s mass, it does not refer to the quality of the gem. Evaluating cut, clarity, and color, as well as carat, is the best way to select a gem. A stone's size or weight can be measured on the metric scale. One carat is the equivalent of 0.2 grams.
When a jewelry item has small diamond chips in it, the measurement may evaluate total carat weight (tcw), rather than giving specific measurements of each chip. Small chips are far less expensive than single larger gems because they are more common.
Most uncut diamonds are considerably larger than cut varieties available through retailers. Uncut diamonds are full of flaws and must be cut to achieve the best looking diamonds. The larger the carat weight of a cut diamond, the more rare and expensive it is. Diamond chips are not particularly expensive, but retailers often employ a listing of tcw to make the article of jewelry seem more impressive. One will notice however, that jewelry including small diamond chips tends to be offered at far lower prices than jewelry with single large stones.
In fact, the value of a diamond or other gem increases dramatically as the stone size increases in weight. A half carat diamond may cost about a fourth the price of a carat diamond. Price increase is due to the rarity of unflawed larger stones.
Jewelers are quick to assure potential customers that size matters. However, the cut and clarity of diamond, along with its setting, may make a small diamond seem larger. A one-carat diamond that is full of flaws may not be as impressive as a half-carat diamond that is close to perfect. Each flaw decreases the ability of the stone to reflect light, so flawed gems are less sparkly.