Amethyst - Moh's Hardness 7. one of the world's best known and loved gemstones, and the most valuable of the quartz's, is also known as the birthstone for February. Amethyst, was restricted for wear and ownership to royalty only, during the middle ages. Its' name comes form a greek derivation, meaning 'not drunken', so named because it was thought to prevent its wearer from becoming intoxicated. It has some treatments to modify its color, heat will change it to the citrine variety, and faded amethyst can sometimes be restored from X-ray radiation. The coloring agent is iron, and changes in its valence state effect the exhibited color.

Ametrine - Moh's Hardness 7. Another variety of Quartz, also known as Trystine, this stone has both colors of yellow (citrine) and violet (amethyst). Most commercial deposits are in Brazil and Bolivia.

Aquamarine - See Beryl.

Beryl - Moh's Hardness 7.5-8. Precious Beryl has at least 2 well known varieties in its family and several others that although lesser known are still quite valuable. Varying in size, color and cost there is likely to be one just right for you. Here are the better known and more valuable names:
      Aquamarine - Lt. Blue to Dark Blue, blue-green.
      Bixbite - Raspberry Red
      Emerald - Emerald Green, Green, slightly yellowish green
      Golden Beryl - Lemon-yellow to golden yellow
      Heliodor - Light yellow-green.
      Morganite - Pink, peach to violet, salmon color

Citrine - Moh's Hardness 7. The name comes from its color. Natural citrine is very rare, most occurs from the heat treatment of amethyst. Some variations have orange and red tints, and are often linked to a regional mine name to coordinate with the color, e.g. "Madeira Citrine" for red to reddish orange citrines.

Emerald - see Beryl

Garnet - Moh's hardness 6-7.5. This is actually a group name for a series of gem and non-gem garnet species. The name garnet is usually used in reference to either Pyrope or Almandite.  Also, it is commonly thought of as being red, but actually occurs in a wide variety of colors including, red, green, yellow, brown, black, orange, rose, colorless, emerald green, &yellow-green.
    Some of the species listed below:
      Pyrope - Red with Brown tint
      Almandite - Red with violet tint
      Rhodolite - Purplish Red, Rose, or Raspberry
      Spessartite - Orange to red-brown
      Tsavorite - Green to Emerald Green
      Demantoid - yellow-green to emerald green {the most valuable of all garnets}

Indicolite - see Tourmaline

Iolite - Moh's Hardness 7-7.5.  Also known as Cordierite and Dichroite. The color is usually blue but since this stone is so highly dichroic (different colors when viewed in different orientations), it can also appear, violet or brown - that depends on how it was oriented when it was cut.

Ruby - Moh's Hardness 9. The red gem variety of the mineral corundum this is the second hardest natural stone. Red to Blood Red, with the most valuable color's referred to as Pigeon Blood Red. Related to sapphire.

Sapphire - Moh's hardness 9. Another gem variety of the corundum family. Sapphires occur in every color except red, that is reserved for Ruby.

Topaz - Moh's Hardness 8-8.5. Topaz occurs in a variety of colors, including brown, light blue, medium blue, dark blue, pink, peach, orange, orange-red, yellow, & maroon. The most expensive varieties are pink to orange, called Precious Topaz, and intense Orange with Red Tones in the basal axis, called Imperial Topaz.

Tourmaline - Moh's Hardness of 7-7.5. One of the largest variations of color can be found with this stone. It has widespread occurrences throughout the world, but some localities are 'mined' out, other's have unique characteristics that may make those stones particularly valuable. But no matter where they originate, tourmalines have some unusual characteristics as well as a great variety of color - they sometimes exhibit zoned color within the same crystal - red cores with green rinds form what is called the "watermelon tourmaline". They exhibit two other characteristics, they are both piezoelectric and pyroelectric, and will produce electrical energy when heated or rubbed.