GI 13: Separating Red, Pink, and Purple Gems

Question 1

What is the most widely known transparent purple gem?

Answer 1

Amethyst Quartz

Question 2

You would identify a transparent, deep pink, DR gem with an RI of 1.62 and 1.64 and a birefringence of .020 as

Answer 2

Pink Tourmaline

Question 3

How come garnets don’t show birefringence or pleochroism?

Answer 3

Because they are SR

Question 4

Like natural corundum, both flux and hydrothermal synthetic corundum might display what?

Answer 4

Angular growth features

Question 5

You would identify a transparent, red-orange, SR stone with an RI of 1.72 and a chromium spectrum as what?

Answer 5

Red Spinel

Question 6

The most useful gemological tool for distinguishing natural from synthetic corundum is what?

Answer 6

Microscope

Question 7

You would identify an opaque, orange-red gem with a wavy, fibrous structure and birefringence blink as

Answer 7

Calcareous Coral

Question 8

The fastest and least expensive synthetic crystal growth method is

Answer 8

Flame Fusion

Question 9

When certain chemical elements substitute for one another in garnet’s crystal structure, it’s called

Answer 9

Isomorphous replacement

Question 10

Which variety of garnet always has some orange color?

Answer 10

Spessartite

Question 11

One of the best ways to determine if a pink stone is a tourmaline or a topaz is to observe

Answer 11

Birefringence

Question 12

Which of the following gems will usually display birefringence blink in the refractometer?

a. Rhodonite
b. Rose quartz
c. Rhodochrosite
d. Rhodolite garnet

Answer 12

c. Rhodochrosite

Question 13

The 2 characteristics that separate sugilite from charoite are what?

Answer 13

1. RI
2. Appearance

Question 14

You would identify a transparent, light pink, biaxial gem with an RI of 1.66 to 1.67 as

Answer 14

Kunzite Spodumene

Question 15

One of the best ways to determine if a pink stone is a sapphire or a tourmaline is to observe its

Answer 15

RI

Question 16

What are the 3 most popular transparent red-to-pink natural gems?

Answer 16

1. Corundum
2. Garnet
3. Tourmaline

Question 17

What are the 2 factors that distinguish corundum from most other DR gems?

Answer 17

1. RI of 1.76 to 1.77
2. Birefringence of .008

Question 18

What are 3 key indicators of heat treatment in corundum?

Answer 18

1. discoid fractures
2. melt relics
3. broken silk

Question 19

What is the fastest and least expensive growth method for creating synthetic corundum?

Answer 19

Melt: Flame Fusion

Question 20

What are 2 typical features of flame-fusion synthetic corundum?

Answer 20

1. curved growth
2. gas bubbles

Question 21

Why is it a challenge to separate synthetics created by the pulling process from other gems?

Answer 21

Because they can be almost inclusion-free

Question 22

What does both flux and hydrotherm synthetic corundum display that look similar in natural gems?

Answer 22

Angular growth

Question 23

How can you distinguish difference between fingerprints in natural v. synthetic corundum?

Answer 23

the flux fingerprint inclusions have higher relief than natural

Question 24

What is an indicator of hydrothermal synthetic corundum?

Answer 24

chevron growth patterns under magnification

Question 25

What causes garnets to show an RI between 1.72 and OTL?

Answer 25

Isomorphous replacement

Question 26

What do red garnets show in spectrascope?

Answer 26

characteristic iron absorption spectrum

Question 27

How can you identify rhodolite? List 3 factors

Answer 27

1. Purple to purplish red color 2. Absorption Spectrum 3. RI between 1.75 and 1.78

Question 28

What distinguishes Beryl from other gems? Also list the gems.

Answer 28

RI 1.57 to 1.58 1. Corundum (1.76-1.77) 2. Topaz (1.63 to 1.64) 3. Spodumene (1.66 to 1.67) 4. Tourmaline (1.62-1.64)

Question 29

What 2 factors distinguishes calcareous coral from imitation coral?

Answer 29

1. birefringence blink 2. wavy fibrous structure

Question 30

What distinguishes glass from many DR gems it imitates?

Answer 30

It's SR nature

Question 31

What 2 factors distinguishes Kunzite from other DR gems?

Answer 31

1. RI of 1.66 to 1.67 2. Biaxial Optic character

Question 32

What 2 factors distinguishes Rhodochrosite from Rhodonite?

Answer 32

1. Distinctive banded appearance 2. Birefrigence blink

Question 33

What 2 factors distinguishes Amethyst from other transparent purple gems?

Answer 33

1. RI of 1.54-1.55 2. Constant .009 birefrigence

Question 34

What 2 absorption features do Spessartite garnets often show in their spectra?

Answer 34

1. Manganese 2. Iron

Question 35

What 3 factors distinguishes Tourmaline from other gems?

Answer 35

1. RI of 1.62-164 2. Birefringence of 0.020 3. strong dichroism