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GIA-Colored Stones > GI 13: Separating Red, Pink, and Purple Gems > Flashcards

GI 13: Separating Red, Pink, and Purple Gems Flashcards

1
Q

What is the most widely known transparent purple gem?

A

Amethyst Quartz

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2
Q

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

A

Pink Tourmaline

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3
Q

How come garnets don’t show birefringence or pleochroism?

A

Because they are SR

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4
Q

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

A

Angular growth features

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5
Q

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

A

Red Spinel

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6
Q

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

A

Microscope

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7
Q

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

A

Calcareous Coral

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8
Q

The fastest and least expensive synthetic crystal growth method is

A

Flame Fusion

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9
Q

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

A

Isomorphous replacement

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10
Q

Which variety of garnet always has some orange color?

A

Spessartite

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11
Q

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

A

Birefringence

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12
Q

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

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

A

c. Rhodochrosite

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13
Q

The 2 characteristics that separate sugilite from charoite are what?

A
  1. RI
  2. Appearance
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14
Q

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

A

Kunzite Spodumene

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15
Q

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

A

RI

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16
Q

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

A
  1. Corundum
  2. Garnet
  3. Tourmaline
17
Q

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

A
  1. RI of 1.76 to 1.77
  2. Birefringence of .008
18
Q

What are 3 key indicators of heat treatment in corundum?

A
  1. discoid fractures
  2. melt relics
  3. broken silk
19
Q

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

A

Melt: Flame Fusion

20
Q

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

A
  1. curved growth
  2. gas bubbles
21
Q

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

A

Because they can be almost inclusion-free

22
Q

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

A

Angular growth

23
Q

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

A

the flux fingerprint inclusions have higher relief than natural

24
Q

What is an indicator of hydrothermal synthetic corundum?

A

chevron growth patterns under magnification

25
Q

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

A

Isomorphous replacement

26
Q

What do red garnets show in spectrascope?

A

characteristic iron absorption spectrum

27
Q

How can you identify rhodolite? List 3 factors

A
  1. Purple to purplish red color
  2. Absorption Spectrum
  3. RI between 1.75 and 1.78
28
Q

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

A

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)
29
Q

What 2 factors distinguishes calcareous coral from imitation coral?

A
  1. birefringence blink
  2. wavy fibrous structure
30
Q

What distinguishes glass from many DR gems it imitates?

A

It’s SR nature

31
Q

What 2 factors distinguishes Kunzite from other DR gems?

A
  1. RI of 1.66 to 1.67
  2. Biaxial Optic character
32
Q

What 2 factors distinguishes Rhodochrosite from Rhodonite?

A
  1. Distinctive banded appearance
  2. Birefrigence blink
33
Q

What 2 factors distinguishes Amethyst from other transparent purple gems?

A
  1. RI of 1.54-1.55
  2. Constant .009 birefrigence
34
Q

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

A
  1. Manganese
  2. Iron
35
Q

What 3 factors distinguishes Tourmaline from other gems?

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

GIA-Colored Stones (10 decks)

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