Gemology & Mineralogy Fundamentals Flashcards

Which of the following is a polymorph of diamond?

Answer: Graphite

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

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

Answer: The separation of white light into spectral colors

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

Diamond's dispersion value is approximately:

Answer: 0.044

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

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

Answer: Diamond

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

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

Answer: Boron substituting for carbon in the lattice

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

A diamond crystal showing trigons on its octahedral face indicates:

Answer: Resorption or natural etching during ascent

Trigons are triangular etch pits formed by natural dissolution (resorption) as kimberlite magma rises toward the surface and conditions change.

Which diamond type classification is defined by the absence of both nitrogen and boron impurities?

Answer: Type IIa

Type IIa diamonds are chemically the purest, containing no detectable nitrogen or boron, and are often colorless with exceptional transparency.