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GEOREF RECORD

Phase relations in the system Ni-As

R. A. Yund
Phase relations in the system Ni-As
Economic Geology and the Bulletin of the Society of Economic Geologists (November 1961) 56 (7): 1273-1296

Abstract

Phase relations in the system Ni-As were determined in rigid silica-glass tubes, in collapsible Au tubes, and by differential thermal analyses. The system includes the well established minerals maucherite (Ni (sub 11) As (sub 8) ), niccolite (Ni (sub 1) + or -xAs), and NiAs (sub 2) polymorphs rammelsbergite and pararammelsbergite. A phase with the composition of Ni (sub 3) As (dienerite) could not be synthesized, and if this phase exists it must be stable only below 200 degrees C. Ni (sub 5) -xAs (sub 2) is stable to approximately 993 degrees C. and has a large variation in its Ni/As ratio. Maucherite, which is essentially restricted to Ni (sub 11) As (sub 8) composition, melts incongruently at 830 degrees + or -5 degrees C. to niccolite plus a liquid. The existence of a metastable form of Ni (sub 11) As (sub 8) appears to be likely. Niccolite, which is stable to 962 degrees + or -3 degrees C., also has a large variation in its Ni/As ratio. The niccolite solvus between NiAs and NiAs (sub 2) is not useful as a geothermometer, however, since it is nearly vertical in the temperature range of geologic interest. The pararammelsbergite-rammelsbergite inversion was found to occur at 590 degrees C. under the vapor pressure of the assemblage when pure NiAs (sub 2) is in equilibrium with niccolite. The inversion temperature is raised 22 degrees C./1000 bars, giving a H of 0.57 Kcal/mole at 590 degrees C. When pure NiAs (sub 2) is in equilibrium with metallic As instead of niccolite, the inversion temperature is approximately 8 degrees C. higher. Investigation of the inversion temperatures of natural specimens of rammelsbergite and pararammelsbergite shows that solid solution of elements such as Fe, Co, and S may lower the inversion by more than 100 degrees C.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 56
Serial Issue: 7
Title: Phase relations in the system Ni-As
Author(s): Yund, R. A.
Pages: 1273-1296
Published: 196111
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
Accession Number: 1961-008670
Categories: Economic geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus., tables
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Update Code: 1961
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