Assignment 24 - Garnet and Spinel

Question 1

How do garnets’ gemological classifications differ from the way they’re sold in the trade?

Answer 1

Gemologists classify garnets by their physical and optical properties, but many dealers sell garnets on the basis of color or origin.

Question 2

How are garnet species related?

Answer 2

Garnets belong to a group of minerals with the same crystal structure but slightly different chemical composition.

Many garnets are mixtures of two or more garnet species.

Question 3

Which green garnet species is the rarest and most valuable?

Answer 3

Tsavorite (Vanadium) and Demantoid (Iron)

Question 4

What are the three most popular garnet colors?

Answer 4

• Green (Tsavorite & Demantoid)
• Orange (Spessartine, Malaya, Hessonite
• Red (Rhodolite, pyrope-almandine)

Question 5

Substitution of one chemical element for another in the crystal structure of a mineral.

Answer 5

Isomorphous replacement

Question 6

A cabochon with a curved, undercut bottom, designed to lighten the tone of the gem material.

Answer 6

Hollowback

Question 7

What better-known gem was spinel often mistaken for?

Answer 7

Many historically important red gems, long identified as ruby, were recognized as spinel in the 1800s.

Question 8

Which spinel varieties are the most valuable?

Answer 8

In general, red spinel is the most desirable, followed by fine cobalt spinel, then by vibrant hot pink and vivid orange stones.

Question 9

What causes the red color in spinel?

Answer 9

In spinel, the higher the chromium content, the stronger the red hue.

Question 10

All garnets have essentially the same

A. inclusions.

B. crystal structure.

C. impurity elements.

D. chemical composition.

Answer 10

B. crystal structure.

Question 11

The most common crystal habit of all garnets is the

A. cube.

B. octahedron.

C. dodecahedron.

D. hexagonal prism.

Answer 11

C. dodecahedron.

Question 11

Mandarin garnet has been used as a trade name for

A. pyrope.

B. tsavorite.

C. andradite.

D. spessartine.

Answer 11

D. spessartine.

Question 12

Demantoid was first discovered in

A. Brazil.

B. Africa.

C. Russia.

D. Sri Lanka.

Answer 12

C. Russia.

Question 13

Horsetail inclusions are found in

A. malaya.

B. tsavorite.

C. demantoid.

D. spessartine.

Answer 13

C. demantoid.

Question 14

Rhodolite is a mixture of

A. pyrope and andradite.

B. pyrope and almandine.

C. spessartine and pyrope.

D. spessartine and andradite.

Answer 14

B. pyrope and almandine.

Question 15

Tsavorite and hessonite are both varieties of

A. pyrope.

B. grossular.

C. andradite.

D. uvarovite.

Answer 15

B. grossular.

Question 16

Spessartine is most commonly found in

A. marble.

B. limestone.

C. pegmatite veins.

D. metamorphic rock.

Answer 16

D. metamorphic rock.

Question 16

The most important source of rhodolite in recent years has been

A. Brazil.

B. Burma.

C. East Africa.

D. the United States.

Answer 16

C. East Africa.

Question 17

The most desirable, vibrant, and rare blue natural spinels are colored by

A. iron.

B. titanium.

C. cobalt and iron.

D. iron and chromium.

Answer 17

C. cobalt and iron.

Question 18

The trade term malaya is used for a pinkish orange garnet that’s a mixture of

A. pyrope and almandine.

B. andradite and spessartine.

C. pyrope, andradite, and almandine.

D. pyrope, spessartine, and almandine.

Answer 18

D. pyrope, spessartine, and almandine.