CDG Gemology & Mineralogy Fundamentals 2 — Questions and Answers
Question 1: What is the chemical composition of diamond?
- Pure carbon (C) (Correct answer)
- Silicon dioxide (SiO2)
- Aluminum oxide (Al2O3)
- Calcium carbonate (CaCO3)
Correct answer: Pure carbon (C)
Diamond is composed entirely of carbon atoms arranged in a cubic crystal lattice structure.
Question 2: Which crystal system does diamond belong to?
- Hexagonal
- Orthorhombic
- Cubic (isometric) (Correct answer)
- Tetragonal
Correct answer: Cubic (isometric)
Diamond crystallizes in the cubic (isometric) system, which accounts for its high symmetry and optical isotropy.
Question 3: What is the specific gravity (SG) range for diamond?
- 2.42–2.45
- 3.50–3.53 (Correct answer)
- 4.00–4.10
- 2.65–2.66
Correct answer: 3.50–3.53
Diamond has a specific gravity of approximately 3.50–3.53, reflecting its dense carbon atomic packing.
Question 4: Which property best describes diamond's cleavage?
- No cleavage
- Perfect cleavage in two directions
- Perfect octahedral cleavage in four directions (Correct answer)
- Conchoidal fracture only
Correct answer: Perfect octahedral cleavage in four directions
Diamond has perfect octahedral cleavage in four directions parallel to the octahedral faces, which jewelers exploit when cleaving rough stones.
Question 5: What type of luminescence does many gem-quality diamonds exhibit under shortwave UV light?
- Phosphorescence only
- No reaction
- Fluorescence, often blue or inert (Correct answer)
- Triboluminescence
Correct answer: Fluorescence, often blue or inert
Many diamonds fluoresce blue (or are inert) under shortwave UV, though fluorescence is more commonly tested under longwave UV.
Question 6: Diamond's refractive index (RI) of approximately 2.417 produces which optical effect?
- Low dispersion and brilliance
- High brilliance due to total internal reflection (Correct answer)
- Double refraction visible to the naked eye
- Strong pleochroism
Correct answer: High brilliance due to total internal reflection
Diamond's high RI of ~2.417 creates a critical angle of about 24.5°, enabling extensive total internal reflection that maximizes brilliance.
Question 7: What is the Mohs hardness rating of diamond?
- 8
- 9
- 9.5
- 10 (Correct answer)
Correct answer: 10
Diamond rates 10 on the Mohs scale, making it the hardest known natural mineral.
CDG Gemology & Mineralogy Fundamentals 2
What is the chemical composition of diamond?