Iran – Nishapur (Neyshabur) Turquoise
Persian turquoise from Neyshabur, Khorasan – the global colour standard; volcanic tuff host, spider-web matrix, Cu-Al phosphate, treatment assessment.
By gemmology.dev editors
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iran persia nishapur neyshabur turquoise phosphate origin/iran
Introduction
Persian turquoise from the Neyshabur (Nishapur) district of Khorasan-e Razavi Province
is historically the most celebrated turquoise in the world – the deposit that defined
the colour "turquoise" as a colour category for Western culture and trade. Production
has continued for at least 2,000 years, making Neyshabur one of the world's longest-
continuously-operating gem sources. Shirdam et al. (2021) provided a comprehensive
review in Gems & Gemology.
Geological Context
Neyshabur turquoise deposit geology:
Host Rock
- Turquoise occurs in hydrothermally altered volcanic tuffs and rhyolitic rocks
within the Neyshabur district - Hydrothermal copper-bearing fluids altered the volcanic host, precipitating
secondary copper-aluminium phosphate (turquoise) in veins, fractures, and
nodules within the altered rhyolite - The Cu source is the volcanic rock suite itself; Al and P from the alteration
system; the reaction occurs under near-surface, low-temperature conditions
Formula
- Turquoise formula: CuAl₆(PO₄)₄(OH)₈·4H₂O
- Colour depends on Cu/Fe ratio: higher Fe shifts colour toward green
- The finest "robah" grade (see below) has the highest Cu relative to Fe
Quality Grades
| Grade | Description | Quality |
|---|---|---|
| Robah (fox-hole) | Even sky blue; no matrix; maximum colour saturation | Highest – rarest |
| Angi (vein) | Vein material; sky blue; some matrix acceptable | High |
| Arabi (Arabic) | Good colour; moderate matrix | Medium |
| Spider-web | Matrix-patterned; mid-grade; commercially desirable | Mid-grade commodity |
The Spider-Web Matrix
Origin Determination
Identifying Persian vs other turquoise origins:
Analytical Methods
- Trace element geochemistry (LA-ICP-MS or EDXRF): Cu, Al, Fe, Zn ratios;
Persian material has characteristic signatures documented by Shirdam et al. (2021) - Raman spectroscopy: Confirms turquoise mineral species (vs dyed howlite,
magnesite, or stabilised materials) - FTIR: Identifies stabilising resin/wax treatment (phosphate vs polymer
absorption bands)
Visual Comparison
- Persian vs Sleeping Beauty (Arizona): Persian more deeply blue, often with
spider-web matrix; Sleeping Beauty pale to medium blue, matrix-free, "cleaner" - Persian vs Chinese (Hubei): Hubei typically more green-blue, heavier
veining; different Cu/Fe/Zn profile - Visual comparison is trade-level guidance only; analytical confirmation required
Treatment – A Critical Issue
Properties
| Property | Value |
|---|---|
| Composition | CuAl₆(PO₄)₄(OH)₈·4H₂O |
| Crystal system | Triclinic; microcrystalline aggregate |
| Hardness | 5–6 (Mohs); lower in porous material |
| SG | 2.60–2.85 |
| RI | 1.61–1.65 (spot reading on curved surface) |
| Fluorescence | Inert to very weak |
| Lustre | Waxy to dull; polish improves appearance |