CGA Gem Identification & Grading Techniques

Question 1

What property is most commonly used to distinguish diamonds from simulants?

Accepted Answer

Refractive index

Answer

The refractive index (RI) is a measure of how much light bends when it passes through a gemstone, and diamonds have a uniquely high RI compared to most simulants. This optical property is a critical diagnostic tool for gemologists, as it allows for precise identification and differentiation. While hardness and luster are also important, RI provides a more definitive distinction for diamonds.

Question 2

What is the primary scale used to measure gemstone hardness?

Accepted Answer

Mohs Scale

Answer

The Mohs Scale of Mineral Hardness, developed by Friedrich Mohs, is the primary scale used in gemology to measure a gemstone's resistance to scratching. It ranks minerals from 1 (softest, like talc) to 10 (hardest, like diamond) based on their ability to scratch softer materials. This scale is essential for identifying gems and understanding their durability for wear.

Question 3

What tool is typically used to examine internal inclusions in gems?

Accepted Answer

10x Loupe

Answer

A 10x loupe is a handheld magnifying glass that provides ten times magnification, making it the standard tool for examining internal inclusions and external blemishes in gems. Its portability and specific magnification are ideal for quickly assessing clarity characteristics that are crucial for grading and identification. While microscopes offer higher magnification, the 10x loupe is the primary and most commonly used tool for this purpose in the field.

Question 4

Which gemstone is typically treated with heat to enhance its color?

Accepted Answer

Sapphire

Answer

Sapphires are frequently treated with heat to enhance or change their color, making existing colors more vibrant or transforming pale stones into desirable hues. This heat treatment is a common and generally accepted practice in the gem industry to improve the gem's appearance and marketability. While other gems can also be treated, sapphire is particularly known for heat treatment for color enhancement.

Question 5

What does 'cut' refer to in the 4Cs of diamond grading?

Accepted Answer

Proportions and finish

Answer

In the 4Cs of diamond grading (Cut, Color, Clarity, Carat Weight), 'cut' refers to how well a diamond's facets interact with light, which is determined by its proportions, symmetry, and polish (finish). A well-cut diamond maximizes its brilliance, fire, and scintillation, making it appear more lively and beautiful. It is distinct from the diamond's shape, which is its outline.

(CGA) Certified Gemologist Appraiser Practice Test

(CGA) Certified Gemologist Appraiser Practice Test

CGA Gem Identification & Grading Techniques