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Zultanite (gem diaspore) crystals as a mineralogical heritage of Turkey
Murat Hatipoglu Dokuz Eylül University, IMYO, Izmir Multidisciplinary Vocational School, Gemmology and Jewelry Program 35160 Buca-Izmir / TURKEY Tel: +90-232-4400707 / 107 Fax: +90-232-4205181 E-mail: [email protected]
Cahit Helvaci Dokuz Eylül University, Faculty of Engineering, Department of Geological Engineering 35160 Buca-Izmir / TURKEY
The mineral diaspore [Al(OH)O] in itself is not rare, and is found throughout northern and eastern Europe. However, the International Colored Gemstone Association (ICA) declared that zultanite (gem variety of the mineral diaspore) crystals are so rare that they worldwide are only found in Turkey. After the first modern geological studies of the metabauxite and emery ores in the Milas (Muğla) region had been done in the early 1950s, the
existence of diaspore crystals with orthorhombic crystalline system in the Ilbir mountains area was discovered by chance. Therefore, they are put in relief the mineralogy importance into geo-conservation discussion, considering as mineralogical heritage of Turkey. The metabauxite deposit including the zultanite crystals is on the Aydın N19-a4 sheet of the 1/25.000 scale topographic map, and is located between the Aegean sea and Bafa lake in the Milas (Mugla) region of SW Turkey in large scale. In addition, the deposit is found in the Kucukcamlik and Buyukcamlik hills of the Ilbir mountains area in detail. The Milas (Muğla) region is, on the other hand, located on the southwestern section of the Menderes crystalline massif, in which Pan-African metamorphosed and Alpine metamorphosed rocks coexist. Thus, geological formation of the diaspore crystal-bearing region is directly related to the geo-tectonic evolution of the Menderes massif, which can be mostly modified by the late Alpine constructional deformation. Zultanite crystals (Fig. 1) have vitreous striated outer surface, and some can grow to large weights up to about 3 kg. However, average gem rough crystals are between 50-400 gr in weight. The crystals show excellent vitreous luster even, even if they are in a rough state. This luster is gained original appearances to the crystals for good exhibit. The unique zultanite crystals in the Mohs’ hardness of 6.5-7 have dominantly olive green and subordinately soil brown colorations, and display cat’s eye chatoyancy and color change as its phenomenal properties. In addition, no treatment is applied to induce this naturally occurring color-change. All transparent crystals have color-change phenomenon (the alexandrite effect), such as olive green color under direct sunlight, scattered daylight, D65 fluorescent lamp and equal energy source E, and carmine color under low wattage tungsten, mercury and quartz lamps. However, the phenomenon can be grouped into three color-change categories in daylight or equivalent illuminations and low watt tungsten illuminations respectively; (1) olive green or soil
brownish and light bordeaux, (2) olive green and lavender-rose, (3) olive green and morellocherry. As a result of these characterizations, many individual zultanite specimens and largesized gem roughs have been obtained by some famous museums and mineral collectors. The existence of these crystals is limited because they are found in only one deposit. In addition, the supply of the zultanite crystals are somewhat limited by difficulty of mining it. Recovery efforts are complicated by the arduous works of separating the zultanite from its ore matrix called diasporic metabauxite, one of the toughest industrial minerals to exploit in mining activities. Thus, this deposit and its vicinity must be protected as a part of the Mediterranean bauxite belt, and must be recognised in the next revision of the World Heritage List by informing the institution ProGeo. Ultimately, these zultanite crystals of the area would be necessary to participate in the UNESCO Global Network of geosites.
Keywords: Zultanite (Diaspore) crystals, Mineralogical heritage, Mediterranean basin, SW Turkey.
Fig. 1. Zultanite (gem variety of the mineral diaspore) crystals [Al(OH)O] are so rare that they worldwide are only found in Turkey.