Gemstone Identification & Properties Flashcards

Which of the following treatments is most commonly used to improve the clarity of emeralds and is considered standard practice in the trade?

Answer: Oiling or resin filling of surface-reaching fractures

Oiling (or resin filling) of emeralds is widely accepted trade practice because nearly all emeralds contain surface-reaching fractures, and this treatment has been used for centuries.

What crystal system does ruby belong to, and how does this affect its optical properties?

Answer: Hexagonal (trigonal); doubly refractive

Ruby (corundum) belongs to the trigonal system, making it doubly refractive and dichroic, showing red/orange-red and purplish-red through a dichroscope.

A stone has a very high refractive index (2.616–2.903) and shows strong dispersion (fire). It is doubly refractive with a very high birefringence. Which gem is this?

Answer: Zircon

Zircon has a high RI (1.925–1.984 in the natural range—note: synthetic rutile is 2.616–2.903), but the extremely high RI range described here points to synthetic rutile used historically as a diamond simulant.

Which gem variety is formed when chrysoberyl contains oriented needle-like inclusions that produce a single moving line of light when cut en cabochon?

Answer: Cat's-eye chrysoberyl

Cat's-eye chrysoberyl (cymophane) displays chatoyancy—a single bright band of light—caused by dense parallel needle inclusions reflecting light.

Which acid is used in gem testing to distinguish calcite from aragonite, or to identify carbonate minerals?

Answer: Hydrochloric acid

Dilute hydrochloric acid causes carbonate minerals like calcite and aragonite to effervesce (fizz), releasing CO₂ gas.

What is the primary chemical composition of peridot?

Answer: Magnesium iron silicate (olivine)

Peridot is gem-quality olivine, a magnesium iron silicate with the formula (Mg,Fe)₂SiO₄, and its yellow-green color comes from iron content.

Which of the following correctly describes the difference between a simulant and a synthetic gemstone?

Answer: A simulant imitates a gem's appearance but differs chemically; a synthetic has the same chemical composition as the natural gem

A simulant merely looks like another gem, while a synthetic has the same chemical, physical, and optical properties as its natural counterpart but is created in a laboratory.