Gemology Certification Gemology Gem Identification Techniques 3 — Questions and Answers
Question 1: Which test is most reliable for distinguishing real pearls from imitation pearls?
- Specific gravity test
- Tooth test (grit sensation) (Correct answer)
- UV fluorescence
- Refractive index measurement
Correct answer: Tooth test (grit sensation)
Rubbing a real pearl against the teeth produces a gritty sensation due to its layered nacre structure, while imitations feel smooth.
Question 2: A gemologist detects strong red fluorescence under long-wave UV in a colorless stone. This is most characteristic of:
- Synthetic cubic zirconia
- Natural diamond (Correct answer)
- Synthetic moissanite
- White topaz
Correct answer: Natural diamond
Approximately 35% of natural diamonds fluoresce blue, but some show red, orange, or yellow fluorescence under UV light.
Question 3: The spectroscope absorption line at 415 nm is a key diagnostic feature for identifying:
- Rubies
- Cape series diamonds (Correct answer)
- Synthetic sapphires
- Alexandrite
Correct answer: Cape series diamonds
The 415 nm absorption line in the violet is a hallmark of Cape series (light yellow) natural diamonds caused by nitrogen aggregates.
Question 4: What does a conoscope (between crossed polars) reveal about a gemstone?
- Its fluorescent color
- Whether it is isotropic, uniaxial, or biaxial (Correct answer)
- Its surface luster type
- Its thermal conductivity
Correct answer: Whether it is isotropic, uniaxial, or biaxial
Conoscopic examination reveals interference figures that allow identification of a stone's optical character (isotropic, uniaxial, or biaxial).
Question 5: Which of the following gemstones is isotropic and will remain dark throughout a 360° rotation under crossed polarizing filters?
- Quartz
- Spinel (Correct answer)
- Peridot
- Tanzanite
Correct answer: Spinel
Spinel crystallizes in the cubic system and is isotropic, meaning it does not split light and stays dark under crossed polars.
Question 6: A stone's refractive index reading on a refractometer moves when the polarizing filter is rotated. This indicates the stone is:
- Amorphous
- Isotropic
- Anisotropic (doubly refractive) (Correct answer)
- Radioactive
Correct answer: Anisotropic (doubly refractive)
Movement of the RI reading with polarizer rotation confirms the stone is anisotropic (doubly refractive), as it has two RI values.
Question 7: Graining lines visible inside a diamond under magnification most likely indicate:
- Laser drill holes
- Plastic filling
- Irregular crystal growth or twinning (Correct answer)
- Synthetic origin
Correct answer: Irregular crystal growth or twinning
Graining lines in diamonds are caused by irregular crystal growth, strain, or twinning during the diamond's natural formation.
Gemology Certification Gemology Gem Identification Techniques 3
Which test is most reliable for distinguishing real pearls from imitation pearls?