Andradite

Andradite is the most is the most lustrous of the Garnets and has several gemstone varieties. The term Garnet describes a group name for several closely related minerals that form important gemstones, and Andradite is an individual member mineral of the Garnet group. Andradite is a common mineral but is usually opaque and not fit for gemstone use; the transparent gemmy forms are rare and valued. The term Andradite is strictly a mineral term and is rarely used in the gem market. The gem forms of Andradite are known by their variety names of Demantoid, Topazolite, and Melanite.
Chemical Formula Ca3Fe3+2Si3O12
Color Red, Green, Yellow, Orange, Brown, Pink, Gray, Black, Multicolored
Hardness 6.5Â -Â 7.5
Crystal System Isometric
Refractive Index 1.888Â -Â 1.889
SG 3.8Â -Â 3.9
Transparency Transparent to opaque
Double Refraction None
Luster Adamantine, submetallic
Cleavage None
Mineral Class Andradite (Garnet)

Andesine

Andesine is a red feldspar gemstone, sometimes with greenish hints and a slight labradorescent effect. Andesine is a relatively new gem on the market. It first appeared in 2003, though its exact origins were never fully disclosed. There are those who believe that a limited deposit of natural red Andesine from an alluvial source in Congo is the origin of this material. Although this is possible, it has yet to be proven. Aside from a possible natural stock from the Congo, the material on the market today is produced in China by artificially enhancing Labradorite through diffusion treatment with copper.
Chemical Formula (Na,Ca)Al1-2Si3-2O8
Color Red, Green, Yellow, Orange, Pink, Multicolored
Hardness 6Â -Â 6.5
Crystal System Triclinic
Refractive Index 1.560Â -Â 1.568
SG 2.69Â -Â 2.70
Transparency Transparent to translucent
Double Refraction .008
Luster Vitreous
Cleavage 2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal.
Mineral Class Plagioclase feldspar (Also see the minerals Andesine and Labradorite))

Andalusite

Andalusite gemstones are remarkable for their fascinating color habits and very strong pleochroism, which can cause a muliticolored effect of shades of yellow, olive-green, and reddish-brown within a single gem. Although Andalusite as a mineral is not uncommon, the transparent variety used as a gem is very rare. Another important form of Andalusite that is entirely different is the mostly opaque Chiastolite variety, which is known for its unique cross-shaped design within the body of a crystal.
Chemical Formula Al2SiO5
Color White, Green, Yellow, Orange, Brown, Pink, Gray, Black, Multicolored
Hardness 7Â -Â 7.5
Crystal System Orthorhombic
Refractive Index 1.62Â -Â 1.65
SG 3.1Â -Â 3.2
Transparency Transparent to opaque
Double Refraction -0.01
Luster Vitreous
Cleavage 2,1
Mineral Class Andalusite

Ametrine

Ametrine is a relatively new gem term, and the word is a combination of Amethyst and Citrine. Ametrine is a unique gemstone in that it is essentially combined of two separate gemstones. Although Amethyst, the purple variety of Quartz, and Citrine, the yellow/orange variety of Quartz belong to the same scientific mineral classification, they have always been distinguished as individual gemstones. The unique color combination of Ametrine has sparked an interest and appeal to this distinctive gemstone.
Chemical Formula SiO2
Color Yellow, Purple, Multicolored
Hardness 7
Crystal System Hexagonal
Refractive Index 1.54Â -Â 1.55
SG 2.63Â -Â 2.65
Transparency Transparent
Double Refraction .009
Luster Vitreous
Cleavage Indiscernible
Mineral Class Quartz

Amethyst

Amethyst is considered one of the primary healing gemstones based on its relatively pure color purple appearance and symmetries. The name derives from the Greek phrase amethystos implying soberness. Although Amethyst is a highly regarded gemstone, the gem value has decreased since large sources were discovered in places like Brazil and South Korea. Amethyst colors range from light to dark purple, and the transparent deep purple colors are the most highly regarded. As a variety of quartz, amethyst is composed mainly of silicate anions.
Chemical Formula SiO2
Color Purple
Hardness 7
Crystal System Hexagonal
Refractive Index 1.54Â -Â 1.55
SG 2.63Â -Â 2.65
Transparency Transparent to translucent
Double Refraction .009
Luster Vitreous
Cleavage Indiscernible
Mineral Class Quartz

Amber

Amber is an organic gemstone mineral formed from polymerization. The mineral is the result of compressed and hardened resin from ancient forests. Known for containing preserved organic fossiles such as insects, the viscous, sticky resin makes a perfect substrate for inclusions. In some cases of Amber with well-preserved organisms included, the gemstones are more highly valued. Amber is typically an orange translucent color, and marble like to behold.
Chemical Formula Amber is composed of complex organic material without any definitive chemical formula. Its inherent substance can also vary depending on its origination.
Color Orange, Honye, Brown, Blue, Red, Green, Yellow
Hardness 2Â -Â 2.5
Crystal System Amorphous
Refractive Index 1.539Â -Â 1.545
SG 1.0Â -Â 1.1
Transparency Transparent to nearly opaque
Luster Resinous
Cleavage None

Amazonite

Amazonite is a translucent to opaque feldspar gemstone with a pretty green color. It is the greenish variety of the mineral Microcline. Amazonite is named after the Amazon River of South America. There are no Amazonite deposits that exist in the Amazon region, so presumably this stone is named to its resemblance in color to the green of the tropical rainforest.
Chemical Formula KAlSi3O8
Color Blue, Green, Purple, Gray, Multicolored
Hardness 6Â -Â 6.5
Crystal System Triclinic
Refractive Index 1.52Â -Â 1.53
SG 2.56Â -Â 2.58
Transparency Translucent to opaque
Double Refraction -.008
Luster Vitreous
Cleavage 2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal
Mineral Class Microcline