Topaz | Gemopedia

Topaz can be both very common (when clear, or in certain colors like brown, which can turn blue when treated) and very rare (when found in natural beautiful colors rare to the species, like pink and red). Topaz's popularity stems from the gem's good wearability and affordability. Topaz is also often altered with special surface treatments to give it unusual colors and iridescent effects, like mystic, ocean, kiwi, and orchid topaz. Topaz is also a popular birthstone, as blue topaz is December's primary birthstone and yellow topaz is a birthstone for November.
Alternate Names
Sherry Topaz, Hyacinth Topaz, Imperial Topaz, Precious Topaz, Swiss Blue, London Blue, Mystic Topaz
Colors
Pale Pink To Strong Red, Purpleish Red, Reddish Purple, Orange Red, Orange, Yellow, Yellowish To Pinkish Yellow, Yellowish Brown, Brown, Light Blue To Dark Greenish Blue, Pale Green, Colorless, Grayish

Topaz Classification

Common Name

Topaz

Species

Topaz

Variety

Colors

Pale Pink To Strong Red, Purpleish Red, Reddish Purple, Orange Red, Orange, Yellow, Yellowish To Pinkish Yellow, Yellowish Brown, Brown, Light Blue To Dark Greenish Blue, Pale Green, Colorless, Grayish

Alternate Names

Sherry Topaz, Hyacinth Topaz, Imperial Topaz, Precious Topaz, Swiss Blue, London Blue, Mystic Topaz

Gemstone Groups

Key Separations

refractive index, birefringence, optic character; possibly specific gravity. The refractive index of blue topaz varieties may be lower than others by as much as 0.01. Some topaz is coated, causing an inert reaction to LWUV and SWUV, different spectra and variable reactions to a CCF test.

Comments

Crystal habit is typically an orthorhombic prism, with rhombic cross-section, basal cleavage and striations along the length of the crystal (c-axis). Misnomers: slave's diamond-colorless topaz, Brazilian sapphire-blue topaz. Sherry topaz: brownish yellow to orange to yellow brown the color of sherry. Hyacinth topaz: dark orange, dark orange-red to reddish brown. Imperial topaz: top color medium reddish orange. Precious topaz: yellow and orange. Sky blue topaz: light blue irradiated topaz. Swiss blue topaz: medium blue irradiated topaz. London blue topaz: darker greenish blue irradiated topaz. Colorless and gray topaz has RI 1.609 to 1.617. Red, pink, purple, orange, yellow and brown stones: RI typically 1.629 to 1.637. Surface treated green stones: RI 1.609 to 1.617. Many times the the stones are long and thin and show pleochroic colors at the far ends of the stone. Birthstone for November

Topaz Optical Properties

Transparency

Transparent

Refractive Index

1.619-1.627
Tolerance:(+0.010/-0.010)

Birefringence

0.008-0.01

Optic Character

Biaxial

Optic Sign

Positive

Polariscope Reaction

Doubly Refractive (DR)

Fluorescence

SWUV: Variable
LWUV: Variable

CCF Reaction

Surface treated green: pink to red

Pleochroism

Dichroic, weak to moderate, varying shades of body color

Dispersion

Strength: weak fire Value: 0.014

Comments

Topaz Chemistry & Crystallography

Chemical Name

fluorosilicate of aluminum with hydroxyl

Chemical Formula

Al2(F,OH)2SiO4

Synthesis

Crystal System

Orthorhombic

Classification

Silicate

Nature

Natural

Crystallinity

Crystalline

Comments

Topaz Characteristic Physical Properties

Hardness

8

Streak

White

Specific Gravity

3.49-3.57 Range:+/-0.04 Typical:3.53

Toughness

Fair

Inclusions

Blue stones have Type I clarity for blue and all other colors are type II clarity. Stones sometimes contain long tube-like cavities containing liquid, healed fractures and areas that look like they are starting to cleave. Stones might include 2-phase and 3-phase inclusions some of which contain more than one liquid that have not been mixed. Stones have a coating on the pavilion or crown of stone There might scratches of treated surface of the stone that show colorless areas underneath. Surface treated green topaz is blue green in appearance and looks spotty there might also be blue color concentrations in surface reaching fractures.

Luster

Vitreous

Stability

Good

Fracture

Conchoidal

Cleavage

Perfect, in one direction

Comments

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