Gemological and Chemical Characterization of Gem-Quality Titanite from Morocco

Yu Yuan; Zhuang Miao; Yi Zhao; Bo Xu; Jialu Gu; Pengyu Yuan

doi:10.3390/cryst14010080

Crystals (Jan 2024)

Gemological and Chemical Characterization of Gem-Quality Titanite from Morocco

Yu Yuan,
Zhuang Miao,
Yi Zhao,
Bo Xu,
Jialu Gu,
Pengyu Yuan

Affiliations

Yu Yuan: Frontiers Science Center for Deep-Time Digital Earth and State Key Laboratory of Geological Processes and Mineral Resources, School of Gemology, China University of Geosciences, Beijing 100083, China
Zhuang Miao: Frontiers Science Center for Deep-Time Digital Earth and State Key Laboratory of Geological Processes and Mineral Resources, School of Gemology, China University of Geosciences, Beijing 100083, China
Yi Zhao: Frontiers Science Center for Deep-Time Digital Earth and State Key Laboratory of Geological Processes and Mineral Resources, School of Gemology, China University of Geosciences, Beijing 100083, China
Bo Xu: Frontiers Science Center for Deep-Time Digital Earth and State Key Laboratory of Geological Processes and Mineral Resources, School of Gemology, China University of Geosciences, Beijing 100083, China
Jialu Gu: Frontiers Science Center for Deep-Time Digital Earth and State Key Laboratory of Geological Processes and Mineral Resources, School of Gemology, China University of Geosciences, Beijing 100083, China
Pengyu Yuan: Frontiers Science Center for Deep-Time Digital Earth and State Key Laboratory of Geological Processes and Mineral Resources, School of Gemology, China University of Geosciences, Beijing 100083, China

DOI: https://doi.org/10.3390/cryst14010080
Journal volume & issue: Vol. 14, no. 1
p. 80

Abstract

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Titanite is a widespread accessory mineral in igneous, metamorphic, and hydrothermal rocks, but few comply with gem-grade requirements. Previous studies on Moroccan titanite focused on elementary composition and U-Pb dating. In this study, two gem-grade titanites (MA-1 and MA-2) from the Moroccan Central High Atlas were investigated through gemological and chemical studies, including infrared spectrum, Raman spectrum, SEM-EDS, and LA-ICP-MS. Two titanite samples are yellow, transparent–translucent with a greasy luster, 3.5 and 2.5 mm long. MA-1 and MA-2 have similar gemological properties, the refractive index (RI) is beyond the range of the refractometer (>1.78), the specific gravity (SG) values fall in the range of 3.52~3.54 and both are inert to short-wave and long-wave UV radiation. The spectral characteristics have high consistency with the RRUFF database. The major elements’ composition shows a negative correlation between Al, Fe, V, and Ti, suggesting the titanites underwent substitutions such as (Al, Fe3+) + (F, OH) ↔ Ti + O. The titanite samples, characterized by a low abundance of REE (802~4088 ppm) and enriched in LREE, exhibit positive Eu (δEu: 1.53~7.79) and Ce (δCe: 1.08~1.33) anomalies, indicating their formation in a hydrothermal environment with low oxygen fugacity. The 238U/206Pb and 207Pb/206Pb ratios of the titanites yield lower intercept ages of 152.6 ± 2.2 and 151.4 ± 5.3 Ma (1s), consistent with their weighted average 206Pb/238U ages of 152.3 ± 2.0 and 150.7 ± 3.2 Ma (1s) respectively. The results of U-Pb dating are matched with the second main magmatic activities in the High Atlas intracontinental belt of Morocco during the Mesozoic to Cenozoic period. Moreover, the two titanite samples have almost no radiational damage. All the results show that the titanite from High Atlas, Morocco, has the potential to be a reference material for LA-ICP-MS U–Pb dating, but further experiments are needed to be sure.

Published in Crystals

ISSN: 2073-4352 (Online)
Publisher: MDPI AG
Country of publisher: Switzerland
LCC subjects: Science: Chemistry: Crystallography
Website: http://www.mdpi.com/journal/crystals/

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