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In situ observations of the transition between beryl and phenakite in aqueous solutions using a hydrothermal diamond-anvil cell

Wang Xian and Li Jiankang
In situ observations of the transition between beryl and phenakite in aqueous solutions using a hydrothermal diamond-anvil cell
The Canadian Mineralogist (December 2020) Pre-Issue Publication

Abstract

Beryl and phenakite are important industrial beryllium minerals. In the hydrous melt of the BeO-Al (sub 2) O (sub 3) -SiO (sub 2) -H (sub 2) O (BASH) system, experiments using quench-type high-temperature and high-pressure equipment have revealed that the different activities of Al (sub 2) O (sub 3) and SiO (sub 2) (alpha Al (sub 2) O (sub 3) and alpha SiO (sub 2) ) are the main factors that lead to different beryllium mineral assemblages. In this study, we attempted in situ observation of the crystallization process of phenakite and beryl in an aqueous solution of the BASH system using a hydrothermal diamond-anvil cell. Experimental results indicate that phenakite and beryl can crystallize faster in this regime (i.e., 2.93-0.58 X 10-5 cm/s in length and 22.39-3.23 mu m3/s in volume) than from a hydrous melt. In addition, in the phenakite and beryl crystallization, pressure-temperature conditions were greater than 467 degrees C and 220 MPa and 495 degrees C and 221 MPa, respectively, and their upper temperatures and pressures attained 845-870 degrees C and 500-1300 MPa. These features indicate that temperature is not the main factor that controls the stability of phenakite and beryl in the BASH system. This stability can be attributed to the diffusion of components in aqueous solution that change alpha SiO (sub 2) and alpha Al (sub 2) O (sub 3) during the heating and cooling processes. During heating, alpha SiO (sub 2) increases while beryl is dissolving, which leads to phenakite crystallization; during cooling, alpha SiO (sub 2) and alpha Al (sub 2) O (sub 3) are sufficient for the remaining beryl to recrystallize. Therefore, the transition between phenakite and beryl in the aqueous solution in the BASH system may be different during heating and cooling processes. This reasoning can explain the abundance of phenakite in miarolitic cavities and the occurrence of phenakite, rather than beryl, in hydrothermally altered pegmatites, volcanic rocks, and other beryllium-rich rocks.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: Pre-Issue Publication
Title: In situ observations of the transition between beryl and phenakite in aqueous solutions using a hydrothermal diamond-anvil cell
Affiliation: China University of Geosciences, State Key Laboratory of Geological Processes and Mineral Resources, Beijing, China
Published: 20201208
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 51
Accession Number: 2021-006896
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. table
Secondary Affiliation: Chinese Academy of Geological Sciences, CHN, China
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202105
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