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A crystal-chemical investigation of clinozoisite synthesized along the join Ca (sub 2) Al (sub 3) Si (sub 3) O (sub 12) (OH)-Ca (sub 2) Al (sub 2) CrSi (sub 3) O (sub 12) (OH)

Mariko Nagashima, Charles A. Geiger and Masahide Akasaka
A crystal-chemical investigation of clinozoisite synthesized along the join Ca (sub 2) Al (sub 3) Si (sub 3) O (sub 12) (OH)-Ca (sub 2) Al (sub 2) CrSi (sub 3) O (sub 12) (OH)
American Mineralogist (October 2009) 94 (10): 1351-1360

Abstract

Cr (super 3+) -bearing clinozoisite along the join Ca (sub 2) Al (sub 3) Si (sub 3) O (sub 12) (OH)-Ca (sub 2) Al (sub 2) Cr (super 3+) Si (sub 3) O (sub 12) (OH) was synthesized using cold-seal pressure vessels at P (sub H (sub 2) O) =0.35 to 0.40 GPa and T=500 degrees C and a piston-cylinder apparatus at P (sub H (sub 2) O) =0.8 to 1.5 GPa and T=500 to 800 degrees C. Gel-starting materials of Ca (sub 2) Al (sub 3-q) Cr (super 3+) (sub q) Si (sub 3) O (sub 12.5) composition with q=1.00, 0.75, 0.50, and 0.25 were employed to maximize the yields of clinozoisite. Mass fractions of clinozoisite in the experimental products with q=0.50, 0.75, and 1 were about 70 to 90% along with lesser amounts of eskolaite, garnet, and quartz. Clinozoisite crystallized from the gel with q=0.25 was associated only with zoisite. The crystal structures of clinozoisite in four runs, containing 0.28, 0.49, 0.50, and 0.62 Cr apfu were refined using X-ray powder diffraction data and the Rietveld method. The amount of Cr (super 3+) at the octahedral M3 and M1 sites ranged from 0.37(1)-0.16(1) to 0.25(1)-0.12(1) apfu, respectively. Corresponding K (sub D) =(Cr (super 3+) /Al) (super M1) /(Cr (super 3+) /Al) (super M3) values range between 0.57 and 0.73. The M2 site contained only Al. The K (sub D) values, and published results for intracrystal-line partitioning in epidote and piemontite, show that the preference of Cr (super 3+) for M1 is stronger than that of Fe (super 3+) and Mn (super 3+) in spite of the fact that most Cr (super 3+) is partitioned into M3. Unit-cell parameters of clinozoisite increase with increasing Cr (super 3+) . Variations in macroscopic unit-cell parameters can be related to variations in the local M3-Oi and M1-Oi distances.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 94
Serial Issue: 10
Title: A crystal-chemical investigation of clinozoisite synthesized along the join Ca (sub 2) Al (sub 3) Si (sub 3) O (sub 12) (OH)-Ca (sub 2) Al (sub 2) CrSi (sub 3) O (sub 12) (OH)
Affiliation: Christian-Albrechts-Universitaet zu Kiel, Institut fuer Geowissenschaften, Kiel, Federal Republic of Germany
Pages: 1351-1360
Published: 200910
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 60
Accession Number: 2010-013947
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
Secondary Affiliation: University of Bern, CHE, SwitzerlandShimane University, JPN, Japan
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201009
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