CBJ Gemstone and Setting Techniques

Question 1

What is the Mohs hardness rating of diamond?

Accepted Answer

10

Answer

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?

Accepted Answer

9

Answer

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?

Accepted Answer

Chromium content causing red color vs. iron and titanium causing blue

Answer

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?

Accepted Answer

5.5–6.5

Answer

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)?

Accepted Answer

Star sapphire

Answer

Star sapphires display asterism—a star-shaped reflection—caused by intersecting needle-like rutile inclusions aligned within the crystal.

(CBJ) Certified Bench Jeweler Practice Test