Turquoise

Turquoise
General
CategoryPhosphate minerals
Formula
(repeating unit)
CuAl6(PO4)4(OH)8·4H2O
IMA symbolTqu[1]
Strunz classification8.DD.15
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H–M symbol)
Identification
ColourTurquoise, blue, blue-green, green
Crystal habitMassive, nodular
CleavagePerfect on {001}, good on {010}, but cleavage rarely seen
FractureConchoidal
Mohs scale hardness5–6
LusterWaxy to subvitreous
StreakBluish white
DiaphaneityOpaque
Specific gravity2.6–2.9
Optical propertiesBiaxial (+)
Refractive indexnα = 1.610
nβ = 1.615
nγ = 1.650
Birefringence+0.040
PleochroismWeak
FusibilityFusible in heated HCl
SolubilitySoluble in HCl
References[2][3][4]

Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. It is rare and valuable in finer grades and has been prized as a gemstone for millennia due to its hue.

Like most other opaque gems, turquoise has been devalued by the introduction of treatments, imitations, and synthetics into the market. The robin egg blue or sky blue color of the Persian turquoise mined near the modern city of Nishapur, Iran, has been used as a guiding reference for evaluating turquoise quality.[5]

  1. ^ Warr, L. N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). New York: John Wiley & Sons. ISBN 978-0-471-80580-9.
  3. ^ Turquoise, Mindat.org, retrieved 2006-10-04. "Turquoise: Turquoise mineral information and data". Archived from the original on 2006-11-12. Retrieved 2006-10-04.{{cite web}}: CS1 maint: bot: original URL status unknown (link).
  4. ^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2000). "Turquoise" (PDF). Handbook of Mineralogy. Vol. IV. Chantilly, Virginia: Mineralogical Society of America. ISBN 978-0-9622097-3-4. Archived (PDF) from the original on 2012-02-11.
  5. ^ "Turquoise Quality Factors". Gemological Institute of America.