24 karat Pure gold is 24 karat, which means that it contains gold in 24 of its 24 parts. Although the terminology seem similar, the karat (k) method for measuring gold purity differs from the carat (c) unit of mass used to weigh diamonds. One carat is equal to 200 milligrams, and one karat is equal to about 29.5 grams. Karats are usually written after the name of a precious metal: 22K gold. But you can also find 14K and 18K gold. The higher the number after the word "karat", the higher the quality. 14K and 18K gold are more expensive than 9K gold because they're higher in quality. 10K gold is the lowest quality and most common type of gold available in retail stores. It's also the cheapest type of gold - one troy ounce of 10K gold costs around $50-100. There are other methods used to measure gold quality. The kimberlite diamond industry uses a rating called "internally flawless". This means that no inclusions or defects can be seen with the naked eye. Diamonds that are internally flawless tend to be more valuable than those that aren't. Other methods include using an electron microscope to look at tiny structures inside the diamond, or testing specific properties of the gold such as its melting point or resistance to corrosion.