Diamond Essentials and Diamond Grading
What this domain tests
Diamond Essentials and Diamond Grading covers diamond formation and properties plus the GIA 4Cs system: color, clarity, cut, and carat weight. Expect questions on grading conditions, clarity characteristics, proportion terminology, fluorescence, and disclosure of treatments and laboratory-grown origin.
Core rules
- Color is graded face-down (table down) in a controlled viewing environment using masterstones, on a D-to-Z scale. Fluorescence is a separate descriptive comment, not part of the color grade.
- Clarity is assessed with a 10× loupe or microscope. Inclusions are internal; blemishes are surface features. The grade runs FL, IF, VVS1–VVS2, VS1–VS2, SI1–SI2, I1–I3, based on size, number, position, nature, and relief.
- Cut grade applies to round brilliant diamonds in the D–Z range: Excellent, Very Good, Good, Fair, Poor. It combines brightness, fire, scintillation, weight ratio, durability, polish, and symmetry; table percentage, crown angle, pavilion angle, depth, girdle, and culet describe proportions.
- Carat weight: 1 carat = 200 mg = 100 points. Price per carat rises sharply at familiar thresholds (0.50, 1.00, 2.00 ct), so a 0.99 ct stone may cost much less than a 1.01 ct stone of the same quality.
- Diamond properties: Mohs hardness 10, perfect cleavage in the {111} directions, SG 3.52, RI 2.417, dispersion 0.044. Hardness does not mean toughness; a sharp blow can cleave a diamond.
- Treatments such as laser drilling and fracture filling, and laboratory-grown origin, must be disclosed.
Worked example
A 1.01 ct round brilliant is graded D, VS2, Excellent cut, with faint blue fluorescence. D is the top color grade, so there is no color deduction. VS2 means small inclusions are noticeable at 10× but not easy to see face-up; it is not eye-clean as a grade, because GIA does not use that term. Excellent cut reflects the proportions, polish, and symmetry. Faint fluorescence is noted but does not automatically lower the color or cut grade. The carat weight just crosses the 1 ct threshold, which usually carries a price premium.
Traps
Do not confuse clarity with cut, or call a stone eye-clean instead of assigning a clarity grade. Do not grade color face-up or under random lighting. Do not assume all fluorescence is bad: strong blue can affect appearance, but faint is usually neutral. Watch girdle descriptions (extremely thin can chip; extremely thick adds weight), culet size, and whether a treatment or lab-grown origin is missing from the description.