Gemology Certification Gemology Gem Identification Techniques 3

Question 1

Which test is most reliable for distinguishing real pearls from imitation pearls?

Accepted Answer

Tooth test (grit sensation)

Answer

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:

Accepted Answer

Natural diamond

Answer

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:

Accepted Answer

Cape series diamonds

Answer

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?

Accepted Answer

Whether it is isotropic, uniaxial, or biaxial

Answer

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?

Accepted Answer

Spinel

Answer

Spinel crystallizes in the cubic system and is isotropic, meaning it does not split light and stays dark under crossed polars.

Gemology Certification Practice Test