CGA Diamond Grading & Gemological Science Flashcards
6 cards from real CGA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CGA Diamond Grading & Gemological Science flashcards as text
A gemologist uses a spectroscope to identify a gemstone. What does this instrument measure?
Answer: Absorption of light wavelengths
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.
What is the refractive index (RI) of a diamond?
Answer: 2.42
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.
What is 'dispersion' in gemology?
Answer: The separation of white light into spectral colors
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.'
Which gemological instrument is used to measure a gemstone's specific gravity?
Answer: Hydrostatic balance
A hydrostatic balance measures specific gravity by comparing a gemstone's weight in air to its weight when submerged in water, using Archimedes' principle.
In diamond grading, what is a 'feather'?
Answer: A type of inclusion that appears as a small fracture or crack
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.
What is the Mohs hardness rating of diamond?
Answer: 10
Diamond rates 10 on the Mohs hardness scale, making it the hardest natural substance known, though it can still cleave along crystallographic planes.