CGA CGA Colored Gemstones & Pearl Evaluation 1 — Questions and Answers
Question 1: Which color is considered the most valuable for a ruby?
- Pinkish-red
- Orangy-red
- Vivid red ('pigeon's blood') (Correct answer)
- Dark brownish-red
Correct answer: Vivid red ('pigeon's blood')
The most prized ruby color is 'pigeon's blood' — a vivid, pure red with a slight blue fluorescence, historically associated with rubies from the Mogok Valley in Myanmar.
Question 2: A gemologist wants to distinguish a natural sapphire from a synthetic sapphire. Which characteristic would be most useful?
- Refractive index
- Color zoning and natural inclusions (Correct answer)
- Specific gravity
- Hardness
Correct answer: Color zoning and natural inclusions
Natural sapphires typically show curved or angular color zoning, silk (rutile needles), and other natural inclusions that are absent or different in synthetic sapphires grown in a lab.
Question 3: What is 'pleochroism' in colored gemstones?
- The ability to display different colors when viewed from different angles (Correct answer)
- The fluorescence of a gemstone under UV light
- The dispersion of white light into spectral colors
- The color saturation of a gemstone
Correct answer: The ability to display different colors when viewed from different angles
Pleochroism is the optical phenomenon in which a gemstone displays different colors or shades when viewed from different crystallographic directions due to selective absorption of light.
Question 4: The 'big three' colored gemstones in the jewelry industry are:
- Emerald, sapphire, and tanzanite
- Ruby, emerald, and sapphire (Correct answer)
- Ruby, sapphire, and aquamarine
- Emerald, amethyst, and sapphire
Correct answer: Ruby, emerald, and sapphire
Ruby, emerald, and sapphire are referred to as the 'big three' colored gemstones due to their historical prestige, consumer demand, and typically high market values.
Question 5: What type of inclusion is most characteristic of natural Colombian emeralds?
- Silk (rutile needles)
- Fingerprint inclusions
- 'Jardin' (garden) of three-phase inclusions (Correct answer)
- Growth tubes
Correct answer: 'Jardin' (garden) of three-phase inclusions
Colombian emeralds typically contain three-phase inclusions consisting of a solid crystal, liquid, and gas bubble within the same cavity, collectively called 'jardin' (French for garden).
Question 6: For a CGA appraisal, what does 'treatment disclosure' mean for colored gemstones?
- Disclosing the gem's country of origin
- Informing the client of any enhancements that alter the gem's appearance or durability (Correct answer)
- Revealing the gem's natural color before cutting
- Documenting the gem's refractive index in the appraisal report
Correct answer: Informing the client of any enhancements that alter the gem's appearance or durability
Treatment disclosure requires appraisers to identify and disclose any enhancements (e.g., heat treatment, fracture filling, irradiation) that have altered the gemstone's natural appearance, color, or durability.
CGA CGA Colored Gemstones & Pearl Evaluation 1
Which color is considered the most valuable for a ruby?