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Monday, July 14, 2025
Thursday, June 5, 2025
Comparison of Emeralds from the Chitral District, Pakistan, with other Pakistani and Afghan Emeralds
Comparison of Emeralds from the Chitral District, Pakistan, with other Pakistani and Afghan Emeralds" by Hanser et al. (2023), suitable for gemology students:
๐ท Origin and Location
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Emerald Deposit: Chitral District, north-western Pakistan (discovered in 2021)
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Geological Zone: Outside the traditional “Emerald Belt” (Indus Suture Zone)
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Host Rocks: Quartz- and mica-rich metapelites of the Arkari Formation, intruded by pegmatitic leucogranite
๐ชจ Rock Types and Formation
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Chitral emeralds form in schist-hosted environments
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Hosted in quartz- and mica-rich metamorphic rocks
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Similar to emeralds in Afghanistan's Panjshir and Swat (Pakistan), but geochemically distinct
๐จ Color and Diaphaneity
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Colors: Light green to dark green
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Transparency: Mostly transparent; higher-quality than earlier samples
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Notable: Deeper-colored samples show potential for gem trade
๐ Inclusions
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Chitral Inclusions:
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Two-phase inclusions (gas + liquid)
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Hollow growth tubes (some with yellowish precipitates)
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Surface-reaching inclusions: quartz, plagioclase (andesine/oligoclase), K-feldspar, phlogopite (main dark mica), rare muscovite
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No three-phase inclusions, which is key to distinguishing from Panjshir, Swat, and Laghman emeralds
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Laghman: Biotite and three-phase inclusions
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Swat: Black opaque minerals (spinel, pyrite), talc, carbonate, and mica
๐ฌ Optical & Physical Properties
Property | Chitral Emeralds |
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Refractive Index | 1.580–1.590 |
Birefringence | 0.008–0.009 |
SG | 2.71–2.74 |
UV-Vis-NIR | Strong Fe²⁺ absorption (~830 nm) |
Raman Spectra | Strong Type II H₂O peaks |
๐งช Chemical Composition (Major/Trace Elements)
By EPMA (Oxides, wt.%):
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SiO₂: ~63.6–64.4%
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Al₂O₃: ~15.3–16.1%
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FeO: ~0.45–0.63%
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MgO: ~1.6–1.9%
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Na₂O: ~1.5%
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BeO: Fixed ~13.6%
By LA-ICP-MS (ppm):
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High in:
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Li: 938–1359 ppm (significantly higher than Swat, Panjshir, Laghman)
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Cs: Up to 5782 ppm
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Na: ~11,000–12,000 ppm
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Mg: ~9,000–11,000 ppm
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Low in:
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Mn: ~15–26 ppm
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Ti: ~11–18 ppm
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Zn: ~13–18 ppm
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๐ก Cause of Color
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Chromophores: Chromium (Cr), Vanadium (V), and Iron (Fe)
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Chitral emeralds show:
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Fe²⁺ dominant (responsible for bluish-green tone)
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Moderate Cr and V contents
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Fe₂⁺ feature in UV-Vis (~830 nm) is stronger than Cr³⁺ and V³⁺, indicating schist-hosted genesis
๐งฌ Elements (in ppm)
Element | Range | Characteristic |
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Li | 938–1359 | High – diagnostic for Chitral |
Cs | 1151–5782 | High – separates from Swat |
Cr | 514–1197 | Color contributor |
V | 222–391 | Color contributor |
Na | ~11,000–12,000 | Higher than Khaltaro |
Fe | ~3413–4164 | Bluish-green tint source |
๐ Diagnostic Features for Origin Determination
Property | Chitral vs Others |
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Inclusions | No three-phase; phlogopite-rich |
Fe²⁺ Absorption | Stronger than Cr³⁺ & V³⁺ |
Li & Cs Levels | Significantly higher |
Water Type (Raman) | Dominant Type II H₂O peaks |
Growth Features | Weak zoning; no sawtooth structures |
๐ Summary for Students
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Chitral emeralds are schist-hosted, Fe²⁺-rich, and alkali-rich
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No three-phase inclusions (unlike Panjshir or Swat)
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High levels of Li and Cs make them chemically distinct
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Excellent for origin studies due to inclusion types, spectroscopic patterns, and chemical profiles
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Increasing mining activity in Chitral makes identification increasingly important in gem markets
Origin of Negative Crystals in Gemstones
Wednesday, June 4, 2025
Wednesday, February 26, 2025
Sodalite from Myanmar vs. Afghanistan: A Complete Comparison
Sodalite is a fascinating gemstone known for its vibrant blue hues and unique tenebrescence, the ability to change color under UV light. In recent years, high-quality sodalite (also called hackmanite) has been sourced from Myanmar and Afghanistan. If you are a gem collector, jeweler, or enthusiast looking to understand the differences between these two sources, this comprehensive comparison will help you make an informed choice.
1. General Characteristics
Tenebrescence: Both Myanmar and Afghan sodalite exhibit tenebrescence, allowing them to change color when exposed to UV light.
Transparency: Afghan sodalite is typically more transparent, whereas Burmese sodalite tends to have more inclusions.
2. Transparency & Clarity
Afghan Sodalite: Cleaner, with fewer inclusions and higher transparency.
Burmese Sodalite: More included, often with visible fractures and foreign material.
3. Color and Tenebrescence
Burmese Sodalite: Usually has a deeper, richer purple or violet color.
Afghan Sodalite: Ranges from very light violet to medium purple.
Tenebrescence: Afghan sodalite generally has a stronger tenebrescence effect than Burmese sodalite.
4. UV Fluorescence and Phosphorescence
Afghan Sodalite: Strong yellow to orange fluorescence under long-wave UV, moderate to strong white fluorescence under short-wave UV.
Burmese Sodalite: Weaker fluorescence, typically greenish-yellow in fractures.
Phosphorescence: Afghan sodalite shows stronger phosphorescence than Burmese sodalite.
5. Refractive Index & Specific Gravity
Afghan Sodalite: Refractive index of 1.45 - 1.48.
Burmese Sodalite: Refractive index of 1.47 - 1.48.
Specific Gravity: Burmese sodalite sometimes has a higher SG (up to 2.44) due to the presence of nepheline inclusions.
6. Spectroscopy & Chemistry
Both types contain traces of sulfur, which contribute to tenebrescence.
Afghan sodalite exhibits additional spectral features in UV-Vis-NIR spectra, such as peaks at 410-412 nm, 277 nm, and 313 nm, which are not found in Burmese sodalite.
7. Treatment
Afghan Sodalite: Often oiled to enhance clarity.
Burmese Sodalite: May also undergo oiling, especially after cutting.
Conclusion: Which One Should You Choose?
If you want a gemstone with strong tenebrescence, Afghan hackmanite is the better choice.
If you prefer a deep, rich purple or violet color, Burmese sodalite is ideal.
For higher transparency and fewer inclusions, Afghan sodalite is superior.
If you appreciate UV fluorescence and phosphorescence, Afghan sodalite offers stronger effects.
Final Thoughts
Both Myanmar and Afghan sodalite have their own unique appeal. Whether you’re a gem enthusiast, collector, or jeweler, understanding these differences can help you make a more informed decision. For investment or aesthetic purposes, consider your preference for tenebrescence, clarity, and fluorescence when choosing between these two beautiful varieties of sodalite.
Title: Sodalite from Myanmar vs. Afghanistan – Differences, Color, & Value
Meta Description: Discover the key differences between Burmese and Afghan sodalite, including color, tenebrescence, transparency, UV fluorescence, and treatment.
Wednesday, December 25, 2024
Tuesday, December 24, 2024
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Gemstone MCQs Quiz Test Your Knowledge in Gemology Part 6 1. A 2-carat fine-quality...