CGA Cheat Sheet 2026

The 30 highest-yield CGA facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. A gemologist uses a spectroscope to identify a gemstone. What does this instrument measure? → Absorption of light wavelengths
2. An oil-filled emerald requires special care instructions for the buyer primarily because: → Ultrasonic cleaners, steamers, and solvents can remove or damage the filler
3. Which diamond cutting style maximizes fire and brilliance through triangular and kite-shaped facets? → Brilliant cut
4. Which factor MOST significantly affects the quality of technical outcomes in CGA practice? → The practitioner's training, preparation, and attention to detail
5. Tanzanite is almost universally heat-treated before sale. What color change does this treatment produce? → Brown to blue-violet
6. What should a complete appraisal report include? → All relevant details, methodology, and purpose of appraisal
7. What is 'brilliance' in a diamond? → The total reflection of white light from within and surface of a diamond
8. Which foundational principle is MOST important for success in Certified Gemologist Appraiser? → Commitment to continuous learning, ethical practice, and quality outcomes
9. A CGA appraiser who knowingly fails to disclose a significant gemstone treatment in a written appraisal report is most directly in violation of: → USPAP standards and professional ethics requirements
10. What is the primary purpose of an appraisal report? → To communicate the item’s value and the rationale for it
11. In Certified Gemologist Appraiser practice, what is the CORRECT sequence when performing a technical procedure? → Plan, prepare, execute, verify, and document
12. Which color is considered the most valuable for a ruby? → Vivid red ('pigeon's blood')
13. Which organization publishes internationally recognized disclosure guidelines for gemstone treatments used by the trade? → CIBJO (World Jewellery Confederation)
14. Which term refers to a gemstone’s resistance to scratching? → Hardness
15. Which type of pearl is most valuable and commands the highest prices in the US market? → South Sea pearls
16. What is the significance of defining the 'type of value' in an appraisal? → It clarifies the valuation context and purpose
17. What is 'heat treatment' in the context of sapphires, and must it be disclosed? → A common enhancement that improves color and clarity; must always be disclosed
18. Which instrument is most effective for detecting and identifying oil or resin fillers in emerald fractures in a gemological laboratory? → Fourier Transform Infrared Spectroscopy (FTIR)
19. What is the primary scale used to measure gemstone hardness? → Mohs Scale
20. Which gemological instrument is used to measure a gemstone's specific gravity? → Hydrostatic balance
21. Which gemstone variety is known as 'trapiche,' featuring a star-like pattern with six spokes? → Emerald, ruby, and sapphire can all occur as trapiche varieties
22. What is 'nacre' in pearl grading? → The iridescent calcium carbonate layers that form a pearl
23. What does 'ideal cut' mean in the context of AGS diamond grading? → A cut achieving AGS grade 0 with optimal proportions for light performance
24. Fracture filling in diamonds to improve apparent clarity is most commonly accomplished using which substance? → High-lead-content glass
25. In diamond grading, what is a 'feather'? → A type of inclusion that appears as a small fracture or crack
26. Which of the four Cs is considered the most important factor in determining a diamond's value? → Cut
27. How long should CGA professionals typically retain official documentation? → According to applicable regulatory requirements and organizational policies
28. What is the PRIMARY purpose of maintaining a clear chain of communication in CGA settings? → To ensure accountability, prevent miscommunication, and facilitate timely information flow
29. When a CGA professional encounters an unexpected result during a procedure, the FIRST action should be to: → Stop, assess the situation, and determine whether to proceed or seek guidance
30. What is the primary purpose of hallmarking in precious metals? → To confirm metal purity and authenticity