湖北十堰红褐色条纹绿松石的谱学特征

doi:10.3964/j.issn.1000-0593(2020)11-3639-05

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Abstract Striped turquoise is a kind of popular variety in the turquoise market of Shiyan, Hubei Province. In this paper, a turquoise sample with the light blue-green substrate and reddish brown stripes was studied. Moreover, reddish brown stripes regularly distributed on the light blue-green turquoise substrate. It has been tested by microscopic observation, EDS, micro-laser Raman spectrometer and micro UV-VIS-NIR. The results show that reddish-brown stripes are formed by the regular gathering of nearly round hematite aggregation in turquoise. Hematite particles are fine and disseminated distributed in the form of dots and snowflakes in turquoise. The results of chemical composition test show that the iron content in the strip is higher than that in the substrate, and the FeO_T content in the inclusion minerals is about 56.06%～59.13%. Micro UV-VIS-NIR spectra show the chromogenic ions in the inclusion minerals mainly are Fe³⁺. It can be seen that the weak absorption near 374nm is caused by the d-electron transition of Fe³⁺ (⁶A₁→⁴E(⁴D)), the double absorption near 429 and 418 nm is caused by the d-electron transition of Fe³⁺ (⁶A₁→⁴E, ⁴A₁(⁴G)), and the weak absorption near 475 and 544 nm is caused by the electron transition of Fe³⁺ ([⁶A₁+⁶A₁→⁴T₁(⁴G)+⁴T₁(⁴G)]). The Raman spectrum of inclusion minerals is typical of hematite at 225，296，411，612，659，1 320 cm^-1. The spectroscopic characteristics of inclusion minerals in striped turquoise indicate that the inclusion mineral is hematite. Hematite in the turquoise is the associated mineral in turquoise deposit. The existence of hematite in turquoise can provide data support for the origin identification of turquoise and the origin traceability of ancient turquoise. The periodic appearance of hematite, an inclusion mineral in the Striped turquoise, indicates the instability and periodicity of the formation environment of turquoise.

Key words：Striped turquoise; Hematite; Chemical composition; Raman spectrum; Micro UV-VIS-NIR spectrum

Received: 2019-11-19 Accepted: 2020-03-22

ZTFLH:

P575

Corresponding Authors: YANG Ming-xing E-mail: yangc@cug.edu.cn

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2020)11-3639-05 OR https://www.gpxygpfx.com/EN/Y2020/V40/I11/3639