Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (2) Citing Articles via Google Scholar Google Scholar Articles by BRIGATTI, M. F. Articles by POPPI, L. Search for Related Content GeoRef GeoRef Citation

Crystal structure and chemistry of lithium-bearing trioctahedral micas-3T

¹ Dipartimento di Scienze della Terra dell'Università di Modena e Reggio Emilia, I-41100 Modena, Italy
² United States Geological Survey, Denver, Colorado, 80225, U.S.A.

e-mail: (M.F. Brigatti, corresponding author) brigatti{at}unimo.it(L. Poppi)lpoppi{at}unimo.it

e-mail: dekile{at}usgs.gov

Chemical analyses and crystal structure refinements were performed on lithian siderophyllite-3T crystals from granitic pegmatites of the anorogenic Pikes Peak batholith (Colorado) to characterize the crystal chemistry and relations with trioctahedral lithium-bearing micas showing different stacking sequences. Chemical data show that the studied samples fall on the siderophyllite-polylithionite join, closer to the siderophyllite end-member. Single-crystal X-ray refinements were carried out on three samples (two of which were taken from core and rim of the same crystal) in space-group P3₁12 (the agreement factor, R_obs, varies between 0.034 and 0.036). Mean bond distances and mean electron counts of M1, M2 and M3 octahedral sites indicate an ordered cation distribution with M1 and M3 positions substantially larger than M2. In the sample with the largest iron content, the M2 mean electron count increases as well as the <M2-O> mean distance, whereas <M2-O> remains smaller than <M1-O> or <M3-O>. The tetrahedral cation-oxygen atom mean distances range from 1.614 to 1.638 Å and from 1.663 to 1.678 Å for T1 and T2 sites, respectively, being consistent with Al³⁺ enrichment in the T2 sites. The tetrahedral rotation angle, , is generally small (3.1 4.6°) and decreases with siderophyllite content. As Fe increases, the T1 tetrahedron becomes flatter (112.4 _T1 110.5°), whereas T2 tetrahedron distortion appears unchanged (110.7 _T2 110.9).

Key-words: lithian siderophyllite, crystal structure, chemistry, octahedral occupancy..

This article has been cited by other articles:

				R. A. Fregola, G. Capitani, E. Scandale, and L. Ottolini Chemical control of 3T stacking order in a Li-poor biotite mica American Mineralogist, February 1, 2009; 94(2-3): 334 - 344. [Abstract] [Full Text] [PDF]

				F.-Z. Teng, W. F. McDonough, R. L. Rudnick, R. J. Walker, and M.-L. C. Sirbescu Lithium isotopic systematics of granites and pegmatites from the Black Hills, South Dakota American Mineralogist, October 1, 2006; 91(10): 1488 - 1498. [Abstract] [Full Text] [PDF]