Description

Turquoise

• Turquoise is a mineral species; triclinic crystal system; chemical compositionCuAl(PO4)4(OH)8-5H2O
• Semi- translucent to opaque
• Light to medium blue, greenish blue to green; often mottled, and may show dark splotches or veins of matrix 

Variety and Trade Names:

• Persian – intense, even medium blue, with low porosity, allowing a good polish; considered the finest quality
• American or Mexican – light blue, greenish blue to bluish green; it is somewhat porous
• Egyptian – greenish blue to yellowish green
• spiderweb – turquoise with matrix in weblike patterns 

Identification:

• Optic Character: AGG (DR) 
• Refractive Index: 1.610-1.650, usually 1.61 spot reading 
• Birefringence: usually not detectable 
• Pleochroism: none 
• Ultraviolet Fluorescence: inert to weak greenish yellow (LW), inert (SW)
• Absorption Spectra: occasionally shows two medium to weak bands at 420 and 432 nm (the latter is stronger); may also have a weak band at 460 nm. 
• Cause of Color: blue – copper; green -copper and iron 
• Specific Gravity: 2.76 (+.14, -.36) 
• Polish Luster: waxy to vitreous 
• Fracture: conchoidal or granular, depending on porosity
• Luster: waxy to dull 
• Cleavage: none 
• Identifying Characteristics: often has matrix 
• Crystal Habit: massive
• Hardness: 5-6
• Toughness: fine quality is fair to good; chalky untreated material is poor and easily fractures 

Enhancements: 

• Method: plastic impregnation, sometimes with a colorant added

Effect: produces medium blue from nearly white, very porous material; also improves durability
Prevalence: common
Detection: combination of color and low SG (strong indication), hot point, infrared spectrum, magnification (possibly)
Stability: stable
Special Care Instructions: avoid heat 

• Method: wax impregnation

Effect: seals the pores and deepens the color of porous, light colored material

Prevalence: common
Detection: hot point and magnification, low SG
Stability: wax may pick up dirt and gradually discolor
Special Care Instructions: avoid heat and solvents

• Method: filling cavities with a metal-loaded epoxy, usually a yellowish “pyrite” color
  

Effect: fills cavities and imitates pyrite inclusions
Prevalence: occasional
Detection: magnification, hot point, color and luster
Stability: epoxy filling may separate
Special Care Instructions: avoid solvents 

• Method: surface coating with lacquer, epoxy, etc
  

Effect: to add color or to seal underlying dye or paint
Prevalence: rare
Detection: visual observation, magnification
Stability: variable
Special Care Instructions: avoid heat and solvents

Birthstone Designation(s): 

December, 5:00 am,
Saturday; 11th wedding anniversary

 

Major Source: US. Others: Australia, Chile, China, Iran (historical), Mexico

 

Stone information is reference from

Gem Reference Guide, Published by GIA. ISBN 0-87311-019-6

Gemstones of the World, Published by Sterling Publishing Co., Inc NY, ISBN 1-4027-4016-6

Encyclopedia of GEMSTONE, Published by ISHINSHA CO., LTD. ISBN 978-986-251-831-1