CGC Gemstone Identification & Classification 5

Question 1

Which simple test helps separate natural amber from most plastic imitations?

Accepted Answer

It floats in saturated salt water

Answer

Amber's low SG (about 1.08) lets it float in saturated salt water, while most plastics sink.

Question 2

Which of these is NOT an organic gem material?

Accepted Answer

Lapis lazuli

Answer

Lapis lazuli is a rock made mainly of lazurite, while the others are formed by living organisms.

Question 3

A six-rayed star in sapphire results from rutile needles oriented in how many directions?

Accepted Answer

Three

Answer

Three sets of needles crossing at 60° each produce two rays, giving a six-rayed star.

Question 4

Immersion showing color concentrated at facet junctions and the girdle suggests which treatment in sapphire?

Accepted Answer

Surface diffusion

Answer

Surface diffusion adds color only in a thin outer layer, which concentrates along facet edges.

Question 5

A thermal conductivity diamond tester cannot reliably separate diamond from:

Accepted Answer

Synthetic moissanite

Answer

Moissanite conducts heat almost as well as diamond, so electrical-conductivity or dual testers are needed.

CGC - Certified Gemstone Consultant Practice Test