ویژگی‌های اُپتیکی و شیمی کانی فلوئوریت‌های رنگین از معادن استان مازندران و علل رنگ‌بندی آنها

نوع مقاله : مقاله پژوهشی

نویسندگان

دانشگاه گلستان

چکیده

 فلوئوریت­های رنگین و بی­رنگ از معادن استان مازندران به منظور دستیابی به علل رنگ­بندی آنها به روش­های طیف­سنجی، پرتودهی گاما، گرما­دهی و تجزیه شیمیایی بررسی شدند. همه فلوئوریت­ها در ناحیه فرابنفش جذب نشان دادند اما در بخش مرئی، فلوئوریت بنفش پررنگ در 560 نانومتر و فلوئوریت قهوه­ای پررنگ حدود 433 نانومتر دارای نوار جذبی پهن بودند و انواع بی­رنگ و سفید نوار جذبی نداشتند. پرتودهی فلوئوریت بی­رنگ اولیه با پرتوی گاما افزون بر رنگین نمودن آنها، موجب ایجاد نوار جذبی در طیف مرئی شد. گرما­دهی فلوئوریت­های بنفش پررنگ موجب کاهش رنگ به صورتی کم­رنگ و فلوئوریت بنفش کم­رنگ به بی­رنگ گردید. از نظر شیمیایی، فلوئوریت قهوه‌ای پررنگ و بنفش پررنگ از بیشترین مقدار (1) مجموع غلظت عناصر خاکی نادر (حدود ppm20REEs=Σ)، Y (ppm9 برای  فلوئوریت قهوه‌ای و ppm 5/3 برای فلوئوریت بنفش) و (2) مجموع غلظت عناصر رادیواکتیو U و Th (ppm 8/2 برای فلوئوریت قهوه‌ای و ppm 9/7 برای فلوئوریت بنفش) برخوردار بودند. برپایه این پژوهش، ناراستی­های شبکه­ای در ساختار فلوئوریت ناشی از واپاشی پرتوزاد اورانیوم و توریوم که مراکز رنگ را در شبکه بلوری فلوئوریت سبب می­شوند به عنوان مهمترین عامل ایجاد رنگ در فلوئوریت­های مورد بررسی معرفی شدند که با آزمایش­های پرتودهی گاما و گرمادهی تأیید شد.    

کلیدواژه‌ها

عنوان مقاله [English]

Optical characteristics and mineral chemistry of colored fluorites from the mines of Mazandaran Province, and causes of their coloration

نویسندگان [English]

  • A Makhtoomi
  • Behnam Shafiei Bafti
  • Rahim Lotfi Orimi
چکیده [English]

In order to understand the cause of coloration of fluorites, following experiments (UV-spectroscopy, irradiation by gamma ray and thermal bleaching) carried out on the colored and colorless fluorites from the mines of Mazandaran Province. All colored and colorless fluorites have absorption band in UV part of electromagnetic waves but deep-violet and brown fluorites have an absorption band in visible range, whereas colorless and white varieties have not shown any absorption bands. Irradiation of colorless fluorites by gamma-ray caused a new absorption bands in UV-visible range. Thermal bleaching of the deep-violet fluorite reduced its color to pale-pink color and also pale-violet colored fluorite changes to colorless ones. Chemically, deep-brown and deep-violet fluorites show (1) the maximum total concentration of rare earth elements (ΣREEs= 20 ppm), Y (9 ppm and 3.5 ppm for deep-brown and deep-violet fluorites, respectively) and (2) total concentration of radioactive elements (U+Th= 2.8 ppm and 7.9 ppm for deep-brown and deep-violet fluorites, respectively). Based on this study, lattice defects in crystal structure of fluorites due to U and Th decay were caused the color centers (F-centers) as most important cause of fluorite coloration. This was confirmed by gamma-ray irradiation and color bleaching experiments.

کلیدواژه‌ها [English]

  • Fluorite
  • coloration
  • absorption bands
  • Mineral chemistry

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مجله بلورشناسی و کانی شناسی ایران
دوره 28، شماره 1 - شماره پیاپی 77
فروردین 1399
صفحه 111-124

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سابقه مقاله

  • تاریخ دریافت: 28 اسفند 1397
  • تاریخ بازنگری: 03 خرداد 1398
  • تاریخ پذیرش: 05 تیر 1398

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