Gemology Certification Gemology Mineralogy & Gem Formation 3

Question 1

What distinguishes a 'Type I' diamond from a 'Type II' diamond?

Accepted Answer

Type I contains nitrogen impurities; Type II has little to no nitrogen

Answer

Diamond type classification is based on nitrogen content: Type I stones contain measurable nitrogen, while Type II stones are essentially nitrogen-free.

Question 2

The phenomenon of 'asterism' in star sapphires is caused by:

Accepted Answer

Oriented needle-like rutile inclusions scattering light

Answer

Silk-like rutile needles aligned along crystallographic axes in corundum reflect light into a six-rayed star under a point light source.

Question 3

Which property best distinguishes calcite from quartz when both appear as colorless crystals?

Accepted Answer

Calcite exhibits double refraction visible to the naked eye

Answer

Calcite's strong birefringence causes visible double images through the crystal, a test easily performed without instruments.

Question 4

In the SMECTITE model of gem formation, what role do fluids play?

Accepted Answer

They transport dissolved minerals and deposit gems as they cool or react

Answer

Hydrothermal and magmatic fluids act as transport media, carrying dissolved elements that precipitate as gems when temperature, pressure, or chemistry changes.

Question 5

A gem with a refractive index of 1.76 and strong double refraction is most likely:

Accepted Answer

Peridot

Answer

Peridot (forsterite olivine) has RI values around 1.654–1.690 and strong birefringence; however, among the listed options, peridot's biaxial double refraction is most diagnostic at RI near 1.76 range for high-iron olivine.

Gemology Certification Practice Test

Gemology Certification Practice Test

Gemology Certification Gemology Mineralogy & Gem Formation 3