31 Questions
What is the main reason for the high prices of Paraíba tourmaline?
Attractive, highly saturated hues and strong demand
What is the primary source of large, fine-color peridot?
Myanmar
Why are some tourmaline crystals more valuable as mineral specimens?
Because they have well-formed, fine colors
What is necessary for cutters to achieve the best colors in tourmaline gems?
Orienting finished gems carefully
Why is colorless zircon easily distinguishable from diamond?
Due to its strong double refraction
What is the primary source of the world's gem-quality tourmaline?
Brazil
What is the best way to clean peridot?
With warm water and mild detergent
What causes the extraordinary colors of Paraíba tourmaline?
Traces of copper
What is necessary to handle zircon with care?
Handling with care due to its brittleness
What is true about blue and colorless zircons?
Virtually all have been treated
What is the primary characteristic that all tourmalines share?
The same crystal structure
What is the main purpose of heating and irradiation in tourmaline treatment?
To enhance color
Why are slender proportions often used in fashioning tourmaline gems?
To accommodate the shape of the crystal
What is the result of tourmaline's strong pleochroism?
A gem that requires careful orientation
Which of the following countries is NOT a significant source of tourmaline?
Australia
What is the characteristic that distinguishes colorless zircon from diamond?
Double refraction
Why does zircon require care in handling and wear?
Because of its brittleness
What is the source of the world's commercial calibrated peridot?
Arizona
What is the characteristic that makes some tourmaline crystals more valuable as mineral specimens?
Their well-formed shape
Why is it best to clean peridot with warm water and mild detergent or soap?
To prevent damage from rapid temperature changes
What type of tourmalines are most gem tourmalines?
Elbaites
What is the primary reason for the high demand of Paraiba tourmaline?
Its attractive, highly saturated hues
What treatment is commonly used to enhance the color of tourmaline?
Heating and irradiation
Why do cutters have to orient finished tourmaline gems carefully?
To achieve the best colors
What is the primary source of the world's gem-quality tourmaline?
Brazil
What is the trade name for pink to red elbaite tourmaline?
Rubellite
What is the Indicolite?
Trade term for blue tourmaline
What type of mineral has been broken down from crystalline to a partly amorphous state by emanations from radioactive impurities?
Metamict
What is the term used for a gem that shows color zoning with two or more colors?
Parti-colored
What elbaite gem has color zoning made of a pink central zone surrounded by a green overgrowth?
Watermelon Tourmaline
Which two gems are prone to abrasions ?
Peridot and Zircon
Study Notes
Tourmalines
- Group of minerals with same crystal structure but different chemical and physical properties
- Most gem tourmalines are elbaites that form in pegmatites
- Heating and irradiation are the two most important tourmaline treatments
- Well-formed, fine-color tourmaline crystals are more valuable as mineral specimens than as fashioned gems
- Cutters have to fashion gems with slender proportions due to the shape of many tourmaline crystals
- Strong pleochroism requires careful orientation of finished gems to achieve the best colors
- Brazil is the main supplier of the world's gem-quality tourmaline
Peridot
- Sensitive to rapid temperature changes and chemicals, so clean with warm water and mild detergent or soap
- Sources in Myanmar supply the world with most of its large, fine-color peridot
- Arizona supplies the world with rough for much of its commercial calibrated peridot
Paraíba Tourmaline
- High prices due to attractive, highly saturated hues, extremely restricted supply, and strong demand
- Traces of copper cause its extraordinary colors
Zircon
- Colorless zircon has strong double refraction, easily distinguishable from diamond and synthetic cubic zirconia
- Require care in handling and wear due to brittleness
- Virtually all blue and colorless zircons have been treated
- Nigeria and Mozambique are Africa's most economically important tourmaline sources
Tourmalines
- Group of minerals with same crystal structure but different chemical and physical properties
- Most gem tourmalines are elbaites that form in pegmatites
- Heating and irradiation are the two most important tourmaline treatments
- Well-formed, fine-color tourmaline crystals are more valuable as mineral specimens than as fashioned gems
- Cutters have to fashion gems with slender proportions due to the shape of many tourmaline crystals
- Strong pleochroism requires careful orientation of finished gems to achieve the best colors
- Brazil is the main supplier of the world's gem-quality tourmaline
Peridot
- Sensitive to rapid temperature changes and chemicals, so clean with warm water and mild detergent or soap
- Sources in Myanmar supply the world with most of its large, fine-color peridot
- Arizona supplies the world with rough for much of its commercial calibrated peridot
Paraíba Tourmaline
- High prices due to attractive, highly saturated hues, extremely restricted supply, and strong demand
- Traces of copper cause its extraordinary colors
Zircon
- Colorless zircon has strong double refraction, easily distinguishable from diamond and synthetic cubic zirconia
- Require care in handling and wear due to brittleness
- Virtually all blue and colorless zircons have been treated
- Nigeria and Mozambique are Africa's most economically important tourmaline sources
Tourmalines
- Tourmalines are a group of minerals with the same crystal structure but varying chemical and physical properties.
- Most gem tourmalines are elbaites, forming in pegmatites.
- Heating and irradiation are the two most important tourmaline treatments.
Value and Demand
- Paraíba tourmaline’s high prices result from a combination of attractive, highly saturated hues, extremely restricted supply, and strong demand.
- Well-formed, fine-color tourmaline crystals can be more valuable as mineral specimens than as fashioned gems.
Cutting and Cleaning
- The shapes of many tourmaline crystals force cutters to fashion gems with slender proportions.
- Cutters must orient finished gems carefully to achieve the best colors due to tourmaline’s strong pleochroism.
- Peridot is sensitive to rapid temperature changes and chemicals, requiring cleaning with warm water and mild detergent or soap.
Sources
- Brazil supplies the majority of the world’s gem-quality tourmaline.
- Myanmar is the primary source of large, fine-color peridot.
- Arizona supplies the world with rough for much of its commercial calibrated peridot.
- Nigeria and Mozambique are Africa’s most economically important tourmaline sources.
Zircon
- Colorless zircon’s strong double refraction easily distinguishes it from diamond and synthetic cubic zirconia.
- Traces of copper cause Paraíba tourmaline’s extraordinary colors.
- Virtually all blue and colorless zircons have been treated.
- Zircon requires care in handling and wear due to its brittleness.
Explore the fascinating world of tourmalines, a group of minerals with unique chemical and physical properties, and discover the factors that influence their high prices.
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