When written with a "c", the word "carat" refers to the units used to measure the weight of jewelry stones. When written with a "k", the word "karat" is a qualitative designation used to describe the fineness of a metal. Each jewelry metal is an alloy that contains different metals in various quantities. Pure gold, for example, is too soft to be used for jewelry;for this reason, gold (and some other precious metals) are typically mixed with other metals. The number of carats indicates the amount of precious metal in the alloy. For example, the phrase "14-karat gold" means that 14 units of pure gold are contained within every 24 units of the alloy.

Random chance plays a role in the cultivation of pearls. Sometimes the oyster expels the core that has been inserted into it to stimulate the production of pearls, while at the same time keeping within its shell the piece of fabric that produces mother of pearl. When this occurs, an irregularly shaped pearl (known as a "keshi pearl") is formed. Smaller pearls are no larger than a pinhead, hence the name "keshi", which is the Japanese word for "poppy seeds". Some keshi pearls, however, can grow as large as 10 mm in diameter. Keshi pearls occur in all species of bivalves that are used for pearl cultivation.

The Kimberley mine was once an extremely productive diamond mine in South Africa. The diamonds were mined by the open-pit method between 1871 and 1908. Without the use of machinery, the workers of this mine dug the largest hole ever dug by human hands. Appropriately called the "Great Forum", it measures 460 meters in diameter and its mast is 1,070 meters deep. Today, however, the lower half of the tree is filled with water. Diamonds weighing a total of 14.5 million carats (almost three tons) were mined. The mine was abandoned in 1914 after a short period of underground mining.

The name "Koh-i-Noor" means "Mountain of Light" in Persian and suggests what an extraordinary stone this famous diamond really is. Like the equally legendary Hope Diamond, the Koh-i-Noor traces its provenance to the mines of India. The Koh-i-Noor was first mentioned in 1304, when it had a round shape and supposedly weighed 108 carats. Other sources claim that it actually weighed 186 carats. The gem entered the hands of the Persian conqueror Nadir Shah in 1739:after the country came under British rule, Queen Victoria received the gem in 1850. Reshaped into its current oval shape, the diamond now weighs more than 105 carats. It has been inserted into the crown of the Queen of England and is kept in the Tower of London.

Kunzite, a variety of spodumene, comes in pale pink and pale purple to dark purple tones with a pinkish veil. Kunzite has a bright, vitreous glow. This attractive mineral is relatively delicate. Kunzite is extremely fissile. Brazil leads the world as the leading supplier of kunzite.