Gemological and Chemical Characteristics of Green Tourmaline from Madagascar, Mozambique, and Tanzania

Maytinee KAEWTIP, Phisit LIMTRAKUN

Abstract


Green tourmalines from Madagascar, Mozambique, and Tanzania were investigated for their gemological properties, spectroscopic characteristics, and chemical compositions. The studied specimens were green, bluish green, yellowish green to brownish green, greenish blue, and blue. Their gemological properties were in a typical range of natural tourmaline. Microscopic examination displayed internal features which were normal of inclusion in tourmaline, such as growth tubes, hollow tubes, healed fractures, fluid inclusions, 2-phase (liquid-gas) inclusions, and small fractures. The cause of coloration in green tourmaline was examined by observing their Ultraviolet-visible-near infrared (UV-Vis-NIR) absorption spectra. The samples from Madagascar and Mozambique exhibited the same spectral range. The absorption bands at near 332, 385, 400 and 415 nm were related to Mn2+ from d-d transitions at the octahedral site. The intensity of absorption bands at 720 and 732 nm were attributed to Fe2+ - Fe3+ intervalence charge transfer (IVCT), while strong bands between 918 to 1220 nm were associated with the Fe2+ octahedral in the Y site. The samples from Tanzania displayed absorption spectra at 307 to 628 nm due to V3+ on the octahedral sites (Z-sites) and a weak peak at 417 nm associated with Cr3+. The green tourmalines from this study exhibit intense bands around 1425 nm that are attributed to hydroxyl groups. Fourier Transform Infrared (FTIR) absorption spectra in the range 4000 - 500 cm-1 were used to identified the stretching vibration of Si6O18 rings (1200 - 820 cm-1) and the BO3 (1350 to 1250 cm-1) and hydroxyl groups (3700 to 3400 cm-1) in the structure of tourmaline. Chemical analyses from electron probe micro-analysis (EPMA) revealed that samples from Madagascar and Mozambique had chemical compositions of elbaite end-members (lower in Ca content and richer in Na content), whereas the samples from Tanzania (Ca-Mg rich tourmaline) were of uvite end-members. This study proposes chemical fingerprinting by the Laser Ablation-Inductively coupled plasma-mass spectroscopy (LA-ICP-MS) technique, useful for differentiating green tourmalines from 3 different localities. The Madagascar samples contained Li, Fe, Zn, Ga, Sn, Pb and Bi, the Mozambique samples contained Li, Fe, Zn and Sn, and the Tanzania tourmalines contained Ti, V, Cr and Sr.

Keywords


Tourmaline, green tourmaline, gemological characteristics, chemical characteristics, spectroscopic characteristics

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References


PC Keller. Gemstones of East Africa. Geoscience Press, Arizona, 1992, p. 144.

R Webster. Gems Their Sources, Description and Identification. 5th ed. Butterworth Heinemann, Great Britain, 1994, p. 1026.

K Schmetzer, JH Bernhardt, C Dunaigre and SM Krzemnicki. Vanadium-bearing gem-quality tourmalines from Madagascar. J. Gemmol. 2007; 30, 413-33.

RV Dietrich. The Tourmaline Group. Van Nostrand Reinhold, New York, 1985, p. 300.

J Selway and J Xiong. Microsoft Excel spreadsheets developed by Julie Selway & Jian Xiong, Available at: http://www.open.ac.uk/earth-research/tindle/AGTWebPages/AGTSoft.html, accessed January 2015.

EJ Gubelin and JI Koivula. Photoatlas of Inclusions in Gemstones. Opinio Publishers, Basel, Switzerland, 2005, p.829.

C Castaneda, SG Eeckhout, GM Costa, NF Botelho and ED Grave. Effect of heat treatment on tourmaline from Brazil. Phys. Chem. Mineral. 2006; 33, 307-16.

GR Rossman and SM Mattson. Yellow, Mn-rich elbaite with Mn-Ti intervalence charge transfer. Am. Mineral. 1986; 71, 599-602.

IL Reinitz and GR Rossman. Role of natural radiation in tourmaline coloration. Am. Mineral. 1988; 73, 309-21

BJ Reddy, RL Frost, WN Martens, DL Wain and JT Kloprogge. Spectroscopic characterization of Mn-rich tourmalines. Vib. Spectros. 2007; 44, 42-9.

SM Mattson and GR Rossman. Fe2+-Fe3+ interactions in tourmaline. Phys. Chem. Mineral. 1987; 14, 163-71.

X Liu, X Feng, J Fan and S Guo. Optical absorption spectra of tourmaline crystals from Altay, China. Chin. Opt. Lett. 2011; 9, 083001.

WAD Fonseca-Zang, JW Zang and W Hofmeister. The Ti-influence on the tourmaline color. J. Braz. Chem. Soc. 2008; 19, 1186-92.

MBD Camargo and S Isotani. Optical absorption spectroscopy of natural and irradiated pink tourmaline. Am. Mineral. 1988; 73, 172-80.

GR Rossman. Gems news: The origin of color in tourmaline from Mt. Marie, Maine. Gems Gemol. 2011; 47, 67-8.

K Schmetzer. 1978, Vanadium III als Farbtrager bei naturlichen Silikaten and Oxiden-ein Beitrag zur Kristallchemie des Vanadiums. Thesis, University of Heidelberg, Germany.

K Schmetzer. Absorption spectroscopy and colour of V3+-bearing natural oxides and silicates: A contribution to the crystal chemistry of vanadium. J. Mineral. Geochem. 1982; 144, 73-106.

A Ertl, GR Rossman, JM Hughes, C Ma and F Brandstatter. V3+-bearing, Mg-rich, strongly disordered olenite from a graphite deposit near Amstall, Lower Austria: A structural, chemical and spectroscopic investigation. J. Mineral. Geochem. 2008; 184, 243-53.

Y Ahn, J Seo and J Park. Electronic and vibrational spectra of tourmaline: The impact of electron beam irradiation and heat treatment. Vib. Spectros. 2013; 65, 165-75.

T Hainschwang, F Notari and B Anckar. Trapiche tourmaline from Zambia. Gems Gemol. 2007; 43, 36-46.

DM Dirlam, BM Laurs, F Pezzotta and B William. Liddicoatite tourmaline from Anjanabonoina, Madagascar. Gems Gemol. 2002; 38, 28-53.

M Akizuki, T Kuribayashi, T Nagase and A Kitakaze. Triclinic liddicoatite and elbaite in growth sectors of tourmaline from Madagascar. Am. Mineral. 2001; 86, 364-9.

FC Hawthorne and DJ Henry. Classification of the minerals of the tourmaline group. Eur. J. Mineral. 1999; 11, 201-15.

PJ Dunn, DE Appleman and JE Nelen. Liddicoatite, a new calcium end-member of the tourmaline group. Am. Mineral. 1977; 62, 1121-4.

KI Webber, WB Simmons and AU Falster. Tourmaline from Antandrokomby, Anjanabonoina, and Fianarantsoa pegmatites, Madagascar. Am. Mineral. 2002; 33, 82.

M Superchi, F Pezzotta and E Gambini. Gemological investigation of multicolored tourmalines from new localities in Madagascar. Gems Gemol. 2006; 42, 156.

BM Laurs, JC Zwaan, CM Breeding, WB Simons, D Beaton, KF Rijsdijk, R Befi and AU Falster. Copper-bearing (PARAIBA-type) tourmaline from Mozambique. Gems Gemol. 2008; 44, 4-30.

WB Simmons, BM Laurs, AU Falster, JI Koivula and KI Webber. MT. MICA: A renaissance in Maine’s gem tourmaline production. Gems Gemol. 2005; 41, 150-63.

JE Shigley, RE Kane and DV Manson. A notable Mn-rich gem elbaite tourmaline and its relationship to “tsilaisite”. Aust. Mineral. 1986; 71, 1214-6.

DJ Henry and CV Guidotti. Tourmaline as a petrogenetic indicator mineral: An example from the staurolite-grade metapelites of NW Maine. Am. Mineral. 1985; 70, 1-15.

K Schmetzer and H Bank. East African tourmalines and their nomenclature. J. Gemmol. 1979; 16, 310-1.


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