GI 13: Separating Red, Pink, and Purple Gems Flashcards
What is the most widely known transparent purple gem?
Amethyst Quartz
You would identify a transparent, deep pink, DR gem with an RI of 1.62 and 1.64 and a birefringence of .020 as
Pink Tourmaline
How come garnets don’t show birefringence or pleochroism?
Because they are SR
Like natural corundum, both flux and hydrothermal synthetic corundum might display what?
Angular growth features
You would identify a transparent, red-orange, SR stone with an RI of 1.72 and a chromium spectrum as what?
Red Spinel
The most useful gemological tool for distinguishing natural from synthetic corundum is what?
Microscope
You would identify an opaque, orange-red gem with a wavy, fibrous structure and birefringence blink as
Calcareous Coral
The fastest and least expensive synthetic crystal growth method is
Flame Fusion
When certain chemical elements substitute for one another in garnet’s crystal structure, it’s called
Isomorphous replacement
Which variety of garnet always has some orange color?
Spessartite
One of the best ways to determine if a pink stone is a tourmaline or a topaz is to observe
Birefringence
Which of the following gems will usually display birefringence blink in the refractometer?
a. Rhodonite
b. Rose quartz
c. Rhodochrosite
d. Rhodolite garnet
c. Rhodochrosite
The 2 characteristics that separate sugilite from charoite are what?
- RI
- Appearance
You would identify a transparent, light pink, biaxial gem with an RI of 1.66 to 1.67 as
Kunzite Spodumene
One of the best ways to determine if a pink stone is a sapphire or a tourmaline is to observe its
RI
What are the 3 most popular transparent red-to-pink natural gems?
- Corundum
- Garnet
- Tourmaline
What are the 2 factors that distinguish corundum from most other DR gems?
- RI of 1.76 to 1.77
- Birefringence of .008
What are 3 key indicators of heat treatment in corundum?
- discoid fractures
- melt relics
- broken silk
What is the fastest and least expensive growth method for creating synthetic corundum?
Melt: Flame Fusion
What are 2 typical features of flame-fusion synthetic corundum?
- curved growth
- gas bubbles
Why is it a challenge to separate synthetics created by the pulling process from other gems?
Because they can be almost inclusion-free
What does both flux and hydrotherm synthetic corundum display that look similar in natural gems?
Angular growth
How can you distinguish difference between fingerprints in natural v. synthetic corundum?
the flux fingerprint inclusions have higher relief than natural
What is an indicator of hydrothermal synthetic corundum?
chevron growth patterns under magnification
What causes garnets to show an RI between 1.72 and OTL?
Isomorphous replacement
What do red garnets show in spectrascope?
characteristic iron absorption spectrum
How can you identify rhodolite? List 3 factors
- Purple to purplish red color
- Absorption Spectrum
- RI between 1.75 and 1.78
What distinguishes Beryl from other gems? Also list the gems.
RI 1.57 to 1.58
- Corundum (1.76-1.77)
- Topaz (1.63 to 1.64)
- Spodumene (1.66 to 1.67)
- Tourmaline (1.62-1.64)
What 2 factors distinguishes calcareous coral from imitation coral?
- birefringence blink
- wavy fibrous structure
What distinguishes glass from many DR gems it imitates?
It’s SR nature
What 2 factors distinguishes Kunzite from other DR gems?
- RI of 1.66 to 1.67
- Biaxial Optic character
What 2 factors distinguishes Rhodochrosite from Rhodonite?
- Distinctive banded appearance
- Birefrigence blink
What 2 factors distinguishes Amethyst from other transparent purple gems?
- RI of 1.54-1.55
- Constant .009 birefrigence
What 2 absorption features do Spessartite garnets often show in their spectra?
- Manganese
- Iron
What 3 factors distinguishes Tourmaline from other gems?
- RI of 1.62-164
- Birefringence of 0.020
- strong dichroism
