Questions and Answers
What is the most important factor in determining a stone's desirability, marketability, and value?
Color
What type of reactions can treatment alter or initiate in gems?
Color-Changing charge transfer reactions
What is white light composed of?
Red, orange, yellow, green, blue, and violet light
What is the primary cause of selective absorption in gems?
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What type of gems can exhibit pleochroism?
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What causes the most desirable red and green gem colors?
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What is the effect of heat treatment on unwanted colors in gems?
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Which element causes a greater variety of gem colors than any other?
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What is the relationship between dispersion and RI in gems?
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What is the result of irradiation in gems?
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" RI " or Refractive index is described as ...?
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What cause the same trace element to produce different colors in different gems ?
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What is the primary source of radiant energy that travels in waves?
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What is the role of transition elements in a gem's band gap, helping electrons absorb some visible light wavelengths?
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What is the effect of chemical composition and crystal structure on gem color?
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What is the result of interaction between electrons and visible light in gems?
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What is the purpose of heat treatment in gems?
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What is the characteristic of gems that can exhibit pleochroism?
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What is the result of valence differences in the same gem material?
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What is the relationship between dispersion and refractive index in gems?
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What is the cause of colors produced by charge transfer in gems?
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What is the role of irradiation in gems?
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Study Notes
Factors Affecting Gem Color and Value
- Color is the most important factor affecting a gemstone's desirability, marketability, and value.
- Colors produced by charge transfer are stronger than those caused by dispersed ions.
Light and Electromagnetic Spectrum
- Light is a form of radiant energy that travels in waves.
- Visible light is a small portion of the electromagnetic spectrum.
- White light is a combination of spectral colors: red, orange, yellow, green, blue, and violet.
Gem Color and Absorption
- Most gem color is caused by selective absorption, influenced by chemical composition and crystal structure.
- Interaction of electrons with visible light causes most selective absorption related gem colors.
Transition Elements and Color Centers
- The presence of transition elements adds new energy levels within a gem's band gap, enabling electrons to absorb specific wavelengths.
- Color centers allow selective absorption to take place by lowering the energy required for electron transitions.
- Chromium causes the most desirable red and green gem colors.
- Iron causes a greater variety of gem colors than any other transition element.
Treatment and Pleochroism
- Heat treatment removes unwanted colors by destroying color centers.
- Only doubly refractive gems can be pleochroic.
- Valence differences can cause variations in color intensity in the same gem material.
Dispersion and Refractive Index
- Dispersion is greater in high-RI gems than in low-RI gems.
Factors Affecting Gem Color and Value
- Color is the most important factor affecting a gemstone's desirability, marketability, and value.
- Colors produced by charge transfer are stronger than those caused by dispersed ions.
Light and Electromagnetic Spectrum
- Light is a form of radiant energy that travels in waves.
- Visible light is a small portion of the electromagnetic spectrum.
- White light is a combination of spectral colors: red, orange, yellow, green, blue, and violet.
Gem Color and Absorption
- Most gem color is caused by selective absorption, influenced by chemical composition and crystal structure.
- Interaction of electrons with visible light causes most selective absorption related gem colors.
Transition Elements and Color Centers
- The presence of transition elements adds new energy levels within a gem's band gap, enabling electrons to absorb specific wavelengths.
- Color centers allow selective absorption to take place by lowering the energy required for electron transitions.
- Chromium causes the most desirable red and green gem colors.
- Iron causes a greater variety of gem colors than any other transition element.
Treatment and Pleochroism
- Heat treatment removes unwanted colors by destroying color centers.
- Only doubly refractive gems can be pleochroic.
- Valence differences can cause variations in color intensity in the same gem material.
Dispersion and Refractive Index
- Dispersion is greater in high-RI gems than in low-RI gems.
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