A variety of quartz containing glistening fragments (usually mica, such as fuchsite, but also hematite), which can be cut and polished as a gemstone. Most commonly when the general public encounter this stone it is in the form of green stone beads that can be anywhere from a pale to a medium green colour. Frequently these beads have been treated with oil to make the stone look a darker colour than it would naturally or even dyed to make the colour more attractive. Aventurine can also be other colours but the most common colour is green. Aventurine is a general term that is used by different commercial interests to mean several different kinds of stones (compare Aventurine Feldspar).
Not to be confused with Aventurine glass or goldstone, a synthetic reddish (due to copper inclusions) or greenish (due to chromium) glass used as a "gem" material. 
In general, Aventurine is an excellent stone to use when gridding areas against geopathic stress or to absorb EMF "smog" and other environmental pollutants. Aventurine can help to stabilize one's state of mind when things seem chaotic or out of focus. Feel stuck? Aventurine helps to open up the mind to endless alternatives and possibilities.
Aventurine is a stone of creativity. It also soothes and calms the emotions and can be a great help for reducing stress, especially before and during exams/tests. Aventurine balances Yin/Yang energies and guards against “psychic vampires” from draining one’s energy.
Physically, use Aventurine to help with disorders of the heart, lungs, adrenal glands, and muscles. 
The name aventurine derives from the Italian "a ventura" meaning "by chance".
Aventurine is a feebly translucent, fine-grained to compact variety of Quartzite, the surface of which has a speckled, metallic sheen, usually of a reddish-brown colour, but occasionally yellow, white, blue or green. This appearance is caused by the presence, in the colourless quartz substance, of numbers of enclosures (scales of mica, plates of chrome-mica fuchsite, etc.), which can always be seen with the aid of the microscope, and sometimes with a simple lens, or with the naked eye.
Also known as Indian Jade.
Aventurine-glass is an artificial product which resembles natural aventurine but possesses an even finer appearance. It is a colourless glass in which are embedded numerous small red octahedra, the faces of which are equilateral triangles. The chemical composition of the material, the well-defined crystalline form, together with the red colour and strong metallic lustre of the enclosures, point to the fact that the latter consists of metallic copper. The much lower hardness of aventurine-glass, together with the form of the enclosures, which can be readily made out with a lens, definitely distinguishes it in all cases from natural aventurine and from sunstone. - Precious stones, Max Bauer, 1968, p 503 
You should never buy a lottery ticket without an aventurine in your left pocket. Lady Luck will be in your left pocket. This is the stone of opportunity. Aventurine is known as the stone of chance or luck. If you gamble or play the lotto, keep this stone in your left pocket.
Aventurine is mainly quartz, a quartzite, usually containing mica. It occurs in several colors including green, red and blue.
Green Aventurine is the stone of luck and chance. It is said to increase perception and creative insight. It is a heart chakra stone.
Blue Aventurine is an Aries stone that opens the Third eye chakra. It is a powerful mental healer that increases vitality and a positive outlook. This stone assists in self-discipline and developing inner strength.
Yellow Aventurine opens the Third eye chakra. It is often used to balance emotions and male/female energies.
Red Aventurine opens the Root chakra. It can assist in creativity, and help you to see the possibilities in new opportunities.
It is used to aid nearsightedness. Aventurine has a stabilizing effect on the emotions. It is excellent for teenagers.