CDG Gemology & Mineralogy Fundamentals 3

Question 1

Which of the following is a polymorph of diamond?

Accepted Answer

Graphite

Answer

Graphite and diamond are both pure carbon polymorphs; graphite forms under low-pressure conditions while diamond requires extreme pressure.

Question 2

In gemology, 'dispersion' refers to which property of a gemstone?

Accepted Answer

The separation of white light into spectral colors

Answer

Dispersion is the difference in refractive index between the red and violet ends of the spectrum, producing the 'fire' seen in diamonds.

Question 3

Diamond's dispersion value is approximately:

Accepted Answer

0.044

Answer

Diamond has a dispersion of 0.044 (B–G interval), which is relatively high and contributes to its pronounced fire.

Question 4

The term 'adamantine luster' is most closely associated with which mineral?

Accepted Answer

Diamond

Answer

Adamantine luster, the brightest luster type for non-metallic minerals, is named after the Greek word for diamond ('adamas').

Question 5

What causes Type IIb diamonds to be electrically semi-conductive?

Accepted Answer

Boron substituting for carbon in the lattice

Answer

Type IIb diamonds contain boron impurities that replace carbon atoms, creating electron holes that allow limited electrical conductivity.

(CDG) Certified Diamond Grader Practice Test