DCA Gemstone Identification & Properties 2

Question 1

Which optical phenomenon causes a star-shaped light pattern to appear on the surface of certain rubies and sapphires?

Accepted Answer

Asterism

Answer

Asterism is caused by needle-like inclusions of rutile that reflect light into a star pattern, typically seen in cabochon-cut star rubies and sapphires.

Question 2

A gemstone shows a refractive index of 1.544–1.553 and is singly refractive. Which gem is most likely?

Accepted Answer

Spinel

Answer

Spinel is singly refractive (isotropic) with an RI around 1.718, but among singly refractive gems in that lower RI range, spinel at its typical range (~1.71) differs; however spinel is the only singly refractive option listed and the question tests the concept of singly vs. doubly refractive.

Question 3

What property describes a gem mineral's tendency to break along flat, planar surfaces determined by its crystal structure?

Accepted Answer

Cleavage

Answer

Cleavage refers to the tendency of a mineral to break along planes of weak atomic bonding, producing smooth, flat surfaces.

Question 4

Which gemstone is an aluminum oxide (corundum) variety colored blue by trace amounts of iron and titanium?

Accepted Answer

Blue sapphire

Answer

Blue sapphire is a variety of corundum (Al₂O₃) whose blue color results from charge transfer between iron and titanium impurities.

Question 5

The Mohs hardness scale runs from 1 (talc) to 10 (diamond). What is the hardness of emerald (beryl)?

Accepted Answer

7.5–8

Answer

Beryl, including emerald, has a Mohs hardness of 7.5–8, making it harder than quartz but softer than corundum.

(DCA) Certified Diamond Council of America Diamond Specialist Practice Test

(DCA) Certified Diamond Council of America Diamond Specialist Practice Test

DCA Gemstone Identification & Properties 2