Chakra signifies one of the seven main energy centers in the body. Each of these centers is a high frequency vortex of spinning energy. Balanced chakras are important for the healthy functioning of the body mind system as a synchronistic whole. The chakras correlate to levels of consciousness, developmental stages of life, colors, sounds, and much more.
Gemstones are used at Chakra centers for clearing, revitalizing, and healing. Generally, the stones correspond with the associated color of the chakra.
There are five requirements for crystals to form: ingredients and temperature, pressure, time, and space. Most minerals on Earth are formed when magma rises from the depths of the planet to the surface and then cools. Crystals form from chemical elements present in the liquid rock, somewhat like the way rain turns into snow crystals in the cold. Over time, the structure of some minerals changes under high pressure or high temperatures, producing new kinds of minerals in the process. The rarest and most beautiful may be turned into jewelry. This family of minerals, called gems, groups together some 50 different semiprecious stones, including agate, opal, and jade, and four precious stones.
For more information on chakra please scroll all the way down and click on "Chakra knowledge 101"