CBJ Gemstone and Setting Techniques 1 — Questions and Answers
Question 1: What is the Mohs hardness rating of diamond?
- 7
- 8
- 9
- 10 (Correct answer)
Correct answer: 10
Diamond rates 10 on the Mohs hardness scale, making it the hardest known natural mineral.
Question 2: What Mohs hardness do sapphire and ruby share?
- 7
- 8
- 9 (Correct answer)
- 10
Correct answer: 9
Both sapphire and ruby are varieties of corundum with a Mohs hardness of 9, making them highly durable for everyday wear.
Question 3: What distinguishes a ruby from a blue sapphire at the chemical level?
- Different crystal structure
- Chromium content causing red color vs. iron and titanium causing blue (Correct answer)
- Country of origin
- Different hardness rating
Correct answer: Chromium content causing red color vs. iron and titanium causing blue
Both are corundum (Al₂O₃), but chromium traces cause rubies' red color while iron and titanium produce sapphires' blue color.
Question 4: What is the approximate Mohs hardness range of opal?
- 5.5–6.5 (Correct answer)
- 7–7.5
- 8–8.5
- 9–9.5
Correct answer: 5.5–6.5
Opal has a Mohs hardness of approximately 5.5–6.5, making it more fragile and prone to scratching than most popular gemstones.
Question 5: Which gemstone is famous for displaying asterism (a star effect)?
- Emerald
- Star sapphire (Correct answer)
- Tanzanite
- Aquamarine
Correct answer: Star sapphire
Star sapphires display asterism—a star-shaped reflection—caused by intersecting needle-like rutile inclusions aligned within the crystal.
Question 6: What is the most common treatment applied to commercial sapphires to improve color and clarity?
- Fracture filling with glass
- Surface diffusion
- Heat treatment (Correct answer)
- Irradiation
Correct answer: Heat treatment
Heat treatment is the most widely used enhancement for sapphires, improving color saturation and dissolving silk inclusions.
CBJ Gemstone and Setting Techniques 1
What is the Mohs hardness rating of diamond?