CGA CGA Diamond Grading & Gemological Science 2

Question 1

A gemologist uses a spectroscope to identify a gemstone. What does this instrument measure?

Accepted Answer

Absorption of light wavelengths

Answer

A spectroscope measures the specific wavelengths of light absorbed by a gemstone, producing an absorption spectrum that is unique to each gem variety and aids in identification.

Question 2

What is the refractive index (RI) of a diamond?

Accepted Answer

2.42

Answer

Diamond has an exceptionally high refractive index of 2.42, which is one reason it has such extraordinary brilliance and fire compared to other gemstones.

Question 3

What is 'dispersion' in gemology?

Accepted Answer

The separation of white light into spectral colors

Answer

Dispersion is the ability of a gemstone to separate white light into its spectral colors, which in diamonds produces the flashes of color known as 'fire.'

Question 4

Which gemological instrument is used to measure a gemstone's specific gravity?

Accepted Answer

Hydrostatic balance

Answer

A hydrostatic balance measures specific gravity by comparing a gemstone's weight in air to its weight when submerged in water, using Archimedes' principle.

Question 5

In diamond grading, what is a 'feather'?

Accepted Answer

A type of inclusion that appears as a small fracture or crack

Answer

A feather is a small fracture or break within a diamond that resembles a feather when viewed under magnification, and its size and location affect the clarity grade.

(CGA) Certified Gemologist Appraiser Practice Test

(CGA) Certified Gemologist Appraiser Practice Test

CGA CGA Diamond Grading & Gemological Science 2