Turquoise

Turquoise
Turquoise
General
Category	Phosphate minerals
Formula; (repeating unit)	CuAl6(PO4)4(OH)8·4H2O
IMA symbol	Tqu
Strunz classification	8.DD.15
Crystal system	Triclinic
Crystal class	Pinacoidal (1) ; (same H–M symbol)
Identification
Colour	Turquoise, blue, blue-green, green
Crystal habit	Massive, nodular
Cleavage	Perfect on {001}, good on {010}, but cleavage rarely seen
Fracture	Conchoidal
Mohs scale hardness	5–6
Luster	Waxy to subvitreous
Streak	Bluish white
Diaphaneity	Opaque
Specific gravity	2.6–2.9
Optical properties	Biaxial (+)
Refractive index	nα = 1.610; nβ = 1.615; nγ = 1.650
Birefringence	+0.040
Pleochroism	Weak
Fusibility	Fusible in heated HCl
Solubility	Soluble in HCl
References

Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula Cu Al₆(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]

^ 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.
^ Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). New York: John Wiley & Sons. ISBN 978-0-471-80580-9.
^ 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).
^ 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.
^ "Turquoise Quality Factors". Gemological Institute of America.

[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.

[Hurlbut-2] Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). New York: John Wiley & Sons. ISBN 978-0-471-80580-9.

[mindat-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).

[rruff-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.

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