Gem Identification & Grading Techniques Flashcards
7 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 7 Gem Identification & Grading Techniques flashcards as text
Which spectroscopic absorption feature is diagnostic for identifying chromium as the cause of color in a ruby?
Answer: Doublet lines at 692 and 694 nm
Chromium in ruby produces characteristic doublet lines at approximately 692 and 694 nm in the red region of the spectrum.
A gemologist observes a weak orange-red fluorescence under longwave UV and no reaction under shortwave UV. Which stone is most likely being tested?
Answer: Natural ruby
Natural rubies often show strong to moderate red or orange-red fluorescence under longwave UV, which can help distinguish them from some synthetic counterparts.
When using a polariscope to test a gemstone, an 'ADR' (anomalous double refraction) reading most likely indicates which type of stone?
Answer: A singly refractive stone like garnet showing strain
ADR occurs when a normally singly refractive (isotropic) stone, like a garnet or glass, shows strain birefringence producing irregular extinction patterns.
Which gemstone treatment is most effectively detected by observing 'snow-globe' effect inclusions or feathers that reach the surface under magnification?
Answer: Fracture filling with glass or resin
Fracture-filled stones show characteristic flash effect, flow structures, and feathers reaching the surface where the filler has entered the stone.
What is the primary purpose of using immersion microscopy when grading gemstones?
Answer: To reduce surface reflections and improve visibility of internal features
Immersion in a liquid close to the stone's refractive index minimizes surface reflections, allowing clearer observation of internal inclusions and growth features.
A transparent blue gemstone shows strong dichroism of blue and violet. Which mineral is the most likely candidate?
Answer: Tanzanite
Tanzanite (blue zoisite) is famous for its strong trichroism showing blue, violet, and burgundy/red depending on the viewing direction.
Which grading system component does 'VS1' refer to in the GIA diamond clarity grading scale?
Answer: Very Slightly Included grade 1 — minor inclusions difficult to see under 10× magnification
VS1 (Very Slightly Included 1) denotes diamonds with minor inclusions that are difficult for a skilled grader to see under 10× magnification.