Today the common definition of a gemstone is any precious or semi-precious stone or rock or mineral.

Semi-precious stones are any other rocks, minerals or petrified material that is not classified as precious including agate, topaz, carnelian, jasper, jade and turquoise.

Agate
The mystical birthstone of September and the birthstone for the zodiac sign Gemini. A hard stone formed from layers of quartz it is found in all colors of the rainbow and has patches or concentric bands of color.

Amazonite
A relatively soft stone that varies from bright verdigris green to a bluish green.  

Aventurine
The star sign for Libra and Planetary stone of Taurus. It is a translucent to opaque variety of microcrystalline quartz and ranges in color from green, peach, brown and blue.

Jade
Listed as the mystical birthstone for March and the birthstone for the sun sign Virgo. It has a smooth texture and appears in emerald green (the most valuable), mottled green and white and rarer colors of yellow, pink, purple and black. The range of greens are light to dark.

Jasper
One of the birthstones listed for the sun sign of Virgo, it is also the mystical birthstone for October and found in all colors.

Pearl
The official birthstone of June, it is an organic gem formed inside mollusks such as oysters and mussels. Formed when an irritant such as a tiny stone or piece of sand gets inside the mollusks shell. A lustrous substance called Nacre is secreted around the object to protect the soft internal surface of the mollusk. As layer upon layer of nacre coats the irritant, a pearl is formed. This process can take up to 7 or 8 years.

Quartz
The quartz is the most common mineral on earth. It is a crystalline mineral that comes in many forms including amethyst, rock crystal, rose quartz, tiger's eye and chalcedony (agate, carnelian, aventurine, jasper).

Turquoise
One of the birthstones of December and the planetary stone for Aquarius, Taurus and Sagittarius. The color varies from green and greenish blue to sky blue shades. It is often dyed and stabilized with resins to produce a harder stone which retains its color and polish.   Pure turquoise is a relatively soft stone

Tiger's Eye
The planetary stone for Gemini and a member of the quartz group.