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Learn Gemstones

Alexandrite

  • Color: color change, from bluish green (daylight) to purple, red or brown (incandescent light)
  • Hardness: 8
  • Refractive index: 1.74 – 1.77
  • Density: 3.68 – 3.80
  • Chemical composition: BeAl2O4
  • Crystal structure: orthorhombic
  • Origins: Russia, Brazil, Tanzania, Madagascar, Zambia, Sri Lanka, Burma, India.

Amethyst

  • Color: violet, purple-violet
  • Hardness: 7
  • Refractive index: 1.54 – 1.55
  • Density: 2.65 – 2.66
  • Chemical composition: SiO2
  • Crystal structure: hexagonal
  • Origins: Widespread; main sources are Brazil, Uruguay, Bolivia, Argentina, USA, East Africa, Zambia, Namibia, Madagascar, India, Sri Lanka, Russia, Australia.

Aquamarine

  • Color: blue to bluish green
  • Hardness: 7.5
  • Refractive index: 1.57 – 1.59
  • Density: 2.67 – 2.75
  • Chemical composition: Be3Al2(SiO3)6
  • Crystal structure: hexagonal
  • Origins: Brazil, Madagascar, Mozambique, Russia, India, Sri Lanka, China.

Chrysoberyl

  • Color: blue, green, yellow, brown
  • Hardness: 8.5
  • Refractive index: 1.74 – 1.77
  • Density: 3.68 – 3.80
  • Chemical composition: BeAl2O3
  • Crystal structure: orthorhombic
  • Origins: Brazil, Madagascar, Zimbabwe, Russia, Sri Lanka, India, Burma.

Diopside

  • Color: green, yellow-green, brown, blue, colorless
  • Hardness: 5.5 - 6
  • Refractive index: 1.66 – 1.71
  • Density: 3.25 - 3.55
  • Chemical composition: CaMg(Si2O6)
  • Crystal structure: monoclinic
  • Origins: USA, Brazyl, Austria, Italy, Tanzania, Pakistan, Russia, Sri Lanka, Burma.

Emerald

  • Color: green
  • Hardness: 7.5 – 8
  • Refractive index: 1.57 – 1.59
  • Density: 2.67 – 2.75
  • Chemical composition: Be3Al2(SiO3)6
  • Crystal structure: hexagonal
  • Origins: Columbia, Zambia, Brazil, Madagascar, Russia, India, Pakistan.

Garnet color change

  • Color: color change, from blue, green or greenish yellow to purple, red, brown or orange-yellow.
  • Hardness: 7
  • Refractive index: 1.89
  • Density: 3.80
  • Chemical composition: nesosilicate
  • Crystal structure: isometric
  • Origins: Madagascar.

Garnet malaia

  • Color: orangey yellow, reddish orange, brownish pink.
  • Hardness: 7 –7.5
  • Refractive index: 1.73 – 1.81
  • Density: 3.65 – 4.20
  • Chemical composition: [Mg3+Mn3]Al2(SiO4)
  • Crystal structure: isometric
  • Origins: Madagascar, Tanzania.

Hessonite

  • Color: yellow, orange, red, brown
  • Hardness: 7
  • Refractive index: 1.72 – 1.75
  • Density: 3.65
  • Chemical composition: Ca3Al2(SIO4)3
  • Crystal structure: isometric
  • Origins: Canada, Mexico, Brazil, Tanzania, Madagascar, Sri Lanka
  • Hessonite is a variety of grossular garnet. Big clean specimens are rare. The best stones are orangey red. Stones are generally not treated.

Iolite

  • Color: blue, violet-blue
  • Hardness: 7 – 7.5
  • Refractive index: 1.52 – 1.56
  • Density: 2.53 – 2.78
  • Chemical composition: Mg2Al3(AlSi5O18)
  • Crystal structure: orthorhombic
  • Origins: Brazil, USA, Canada, Madagascar, Sri Lanka, India, Burma.

Kornerupine

  • Color: green, yellow-green, brown, blue-green
  • Hardness: 7
  • Refractive index: 1.66 – 1.69
  • Density: 3.25 - 3.35
  • Chemical composition: (Mg,Fe)4(Al,Fe)6(SiO4,BO4)5(O,OH)2
  • Crystal structure: orthorhombic
  • Origins: Greenland, Tanzania, Madagascar, Kenya, Sri Lanka, Burma, Australia.

Peridot

  • Color: yellowish green, brownish green
  • Hardness: 6.5 – 7
  • Refractive index: 1.64 – 1.69
  • Density: 3.20 – 3.50
  • Chemical composition: (Mg, Fe)[SiO4]
  • Crystal structure: orthorhombic
  • Origins: China, Burma, Pakistan, USA, East Africa, Norway, Egypt.

Phenakite

  • Color: colorless, light yellow, light pinkish or brownish
  • Hardness: 7.5 - 8
  • Refractive index: 1.65 – 1.69
  • Density: 2.95
  • Chemical composition: Be2SiO4
  • Crystal structure: hexagonal
  • Origins: USA, Brazyl, France, Switzerland, Tanzania, Madagascar, Russia, Sri Lanka.

Rhodolite

  • Color: red, purple
  • Hardness: 7 – 7.5
  • Refractive index: 1.73 – 1.77
  • Density: 3.60 – 3.94
  • Chemical composition: Al2(SiO4)3
  • Crystal structure: isometric
  • Origins: Brazil, Tanzania, Zimbabwe, Madagascar, Sri Lanka, India.

Ruby

    • Color: red, purple red
    • Hardness: 9
    • Refractive index: 1.76 – 1.78
    • Density: 3.99 – 4.06
    • Chemical composition: Al2O3
    • Crystal structure: hexagonal
    • Origins: Burma, Sri Lanka, Thailand, Cambodia, Vietnam, Madagascar, Tanzania, Kenya.

Ruby, the red variety of corundum, is the most expensive gemstone after diamonds. The distinctive rubies of “pigeons blood” color from Mogok (Burma) have the highest value. Specimens over 5 ct. as well as eye clean stones are very rare. Heat treatment is usually applied to improve color and reduce small inclusions.

 

Sapphire

  • Color: any color
  • Hardness: 9
  • Refractive index: 1.76 – 1.78
  • Density: 3.99 – 4.00
  • Chemical composition: Al2O3
  • Crystal structure: hexagonal
  • Origins: Burma, Sri Lanka, India, Madagascar, Kenya, Tanzania, Thailand, Cambodia, China, Australia.

Sapphire, a variety of corundum, exists almost in any color. Color of sapphires is the main factor for price estimation. Heat treatment is usually applied to improve color and reduce small inclusions.

Spessartite

    • Color: orangey yellow, orange, red
    • Hardness: 7
    • Refractive index: 1.79 – 1.81
    • Density: 4.14 – 4.20
    • Chemical composition: Mn3Al2(SiO4)3
    • Crystal structure: isometric
    • Origins: USA, Germany, Brazil, Sri Lanka, Burma, Madagascar, Mozambique, Nigeria.

Spessartite is an orange or orangey red variety of garnet. Intense orange stones have highest value. Large specimens are rare. Stones are generally not treated.

Spinel

    • Color: red, orange, yellow, purple, blue, green, grey
    • Hardness: 8
    • Refractive index: 1.71 – 1.92
    • Density: 3.99 – 4.00
    • Chemical composition: MgAl2O4
    • Crystal structure: isometric
    • Origins: Brazil, USA, Madagascar, Sri Lanka, Burma, Thailand, Cambodia, Afghanistan, Russia.

Spinel probably is the most common imitation of sapphire. Spinels with a highest value are purple, red or orangey red and blue. Stones are generally not treated.

Tanzanite

  • Color: blue, violet blue, green, yellow, brownish
  • Hardness: 6,5 - 7
  • Refractive index: 1.69 – 1.70
  • Density: 3.35
  • Chemical composition: Ca2Al3(O/OH/SiO4/Si2O7)
  • Crystal structure: orthorhombic
  • Origins: Tanzania

Topaz

    • Color: blue, yellow, pink, red, brown, green, colorless
    • Hardness: 8
    • Refractive index: 1.60 – 1.64
    • Density: 3.50 – 3.58
    • Chemical composition: Al2[SiO4](F,OH)2
    • Crystal structure: orthorhombic
    • Origins: Brazil, Madagascar, Russia, USA, Mexico, Pakistan.

Most valued color for topazes is orangey pink (imperial topaz from Brazil). Heat treatment is usual for yellowish stones; color of light blue or colorless stones can be enforced by x-ray treatment and heating. Very big clean crystals are common.

Tourmaline

    • Color: wide color range, green, blue, yellow, pink, red, brown, colorless. Bi-color is common.
    • Hardness: 7 – 7.5
    • Refractive index: 1.61 – 1.66
    • Density: 3.01 – 3.25
    • Chemical composition: (NaLiCa)(Fe11MgMnAl)3Al6((OH)4(BO3)3Si6O18)
    • Crystal structure: trigonal
    • Origins: Brazil, Madagascar, Namibia, Zambia, Sri Lanka, Burma, Russia, USA, Afghanistan.

Tourmalines exist in different colors and are known for their bi-color or even tri-color varieties. Most expensive color varieties are intense green, blue and red (see also Tourmaline rubelite section).

Zircon

    • Color: red, orange, purple, green, blue, yellow, brown
    • Hardness: 6 – 7.5
    • Refractive index: 1.78 – 2.01
    • Density: 3.95 – 4.80
    • Chemical composition: ZnSiO4
    • Crystal structure: tetragonal
    • Origins: Tanzania, Kenya, Madagascar, Cambodia, Sri Lanka, Burma, Thailand, Vietnam, Australia.

Zircons exist in a wide range of colors, but the most expensive stones are purple, red and orange. White zircons are also valued probably due to their extremely high “diamond” refraction. Brownish stones from Cambodia are usually heated to obtain an intense blue color.

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