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An unusual beryl from Arizona

Waldemar T. Schaller, Rollin E. Stevens and Richard H. Jahns
An unusual beryl from Arizona
American Mineralogist (1962) 47: 672-699


A bluish beryl from a pegmatite dike in Mohave County, Arizona, differs distinctly from other known beryls in physical properties and chemical composition. The highest measured value of omega for this beryl is 1.610, and the analyzed sample has omega = 1.608, epsilon = 1.599. Only 4 published analyses of beryls with an omega index higher than 1.592 are known, and the highest index heretofore recorded for any beryl, recognized as such, is 1.602. G=2.921. In composition, this mineral differs markedly from other beryls. It has the lowest percentage of SiO (sub 2) and of Al (sub 2) O (sub 3) of any known beryl. It contains 4.69% of oxides of bivalent elements other than Be, chiefly ferrous Fe and Mg. Its content of Cs (sub 2) O, 6.68%, is much greater than that of nearly all other known beryls. On the other hand, its content of Li (sub 2) O, 0.23%, is only about one-tenth of what would be expected for an alkali-rich beryl. The composition and physical properties are incompatible with distinctive compositional trends determined for beryls by Schaller and Stevens. In general the omega index of refraction ranges from 1.570 for low-alkali beryls to 1.592 for high-alkali beryls. Low-alkali beryls are close to the composition indicated by the standard beryl formula Be (sub 3) .Al (sub 2) .Si (sub 6) O (sub 18) . The high-index beryls can be interpreted in terms of the standard beryl formula combined with the Na-Li beryl formula Na.Be (sub 2) Al.AlLi.Si (sub 6) O (sub 18) and its Cs-Li analogue. In various solid solutions of these end-members the atomic ratios of Si and Al do not vary, but increases in Li are accompanied by equal increases in Na or Cs and by equal decreases in Be. In contrast to the compositional trends for most beryls, the Arizona beryl is deficient in Al; it is high in Na and Cs but low in Li, and its Be content is abnormally high for a high-index, high-alkali beryl. These relationships are attributed to the presence of another end-member represented by the generalized formula (Na, Cs).Be (sub 3) .Al(Fe (sub 2+) , Mg).Si (sub 6) O (sub 18) . The Arizona beryl contains more than 50% of this femag end-member.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 47
Title: An unusual beryl from Arizona
Pages: 672-699
Published: 1962
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
Accession Number: 1962-010391
Categories: Mineralogy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus., tables
N31°15'00" - N37°00'00", W115°00'00" - W109°00'00"
Source Note: nos. 5-6
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Bibliography and Index of North American Geology, U. S. Geological Survey, Reston, VA, United States
Update Code: 1962
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