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 Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science 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 BOJAR, H.-P. Articles by WALTER, F. Search for Related Content GeoRef GeoRef Citation

Fluoro-magnesiohastingsite from Dealul Uroi (Hunedoara county, Romania)

¹ Department of Mineralogy, Landesmuseum Joanneum, Raubergasse 10, A-8010 Graz, Austria
² Institute of Earth Sciences, Karl-Franzens-University Graz, Universitätsplatz 2, A-8010 Graz, Austria

^* E-mail: hans-peter.bojar{at}stmk.gv.at

The new mineral fluoro-magnesiohastingsite, ideally (Na,K,Ca)Ca₂(Mg,Fe³⁺,Al,Ti)₅(Si,Al)₈0₂₂F₂ a member of the calcic-amphibole-group, occurs in small cavities of an altered hematite-rich xenolith in the quaternary trachyandesite at Dealul Uroi, Hunedoara county, Romania. Associated minerals are: titaniferous hematite, augite, phlogopite, enstatite, feldspar, tridymite, titanite, fluorapatite, ilmenite and pseudobrookite. The mineral is reddish-brown to yellowish, with a light reddish-brown streak, and has a perfect {110} cleavage. The tenacity is brittle and the Mohs hardness is 6. Optically the mineral is biaxial (+) and weakly pleochroic, = 1.642 (yellow-brown), ß = 1.647 (light brown), = 1.662 (light brown) at 589 nm 2V (meas. and calc.) is 61°, dispersion was not observed. The orientation of ß is parallel to b. The axial plane is (010) ( ^ c = 26°). It is monoclinic, C2/m, with the unit-cell parameters a = 9.871(1) Å, b = 18.006(2) Å, c = 5.314(1) Å, ß = 105.37(1)°, V = 910.7(2) ų, Z = 2. The calculated density is 3.18 g/cm³. The strongest lines in the X-ray powder diffraction pattern (d_obs in Å, (hkl), l) are: 9.008, (020), 27; 8.421, (110), 61; 3.377, (131), 44; 3.271, (240), 61; 3.124, (310), 100; 2.932, (221), 35; 2.805, (330), 28; 2.700, (151), 54.

The crystal structure of fluoro-magnesiohastingsite was refined to R(F) = 0.054 using reflection intensities collected with MoK X-radiation. Refined site-scattering values and considerations of mean bond lengths demonstrated an ordering of Fe³⁺ at M2. Electron-microprobe data and the A site-scattering values show significant Ca (0.19 apfu) together with K and Na at the Am and A2 sites. The site-scattering value and bond-length of 03 to cations indicate that this site is occupied by F, which was indirectly confirmed by infrared spectroscopy. The emp-analyses correspond to the empirical formula: ^A(Na_0.50K_0.22Ca_0.17)_0.89BCa_2.00^c(Mg_4.03Fe³⁺_0.70Al_0.13Ti_0.13)_4.99T(Si_5.89Al_2.11)_8.00O_22.00F_2.00.

Most companion minerals of fluoro-magnesiohastingsite containing fluorine, like phlogopite, fluorapatite and chondrodite, have a X_F = F/(F+OH) > 0.79. Amphiboles of the hosting trachyandesite are fluoro-members (fluoro-edenite to fluoro-magnesiohastingsite) as well but they have a more variable Si/Al-ratio as the xenolith-hosted fluoro-magnesiohastingsites.

Key-words: fluoro-magnesiohastingsite, new mineral, amphibole group, crystal structure, Dealul Uroi, Romania.

This article has been cited by other articles:

				R. Oberti, G. D. Ventura, and F. Camara New Amphibole Compositions: Natural and Synthetic Reviews in Mineralogy and Geochemistry, October 1, 2007; 67(1): 89 - 124. [Full Text] [PDF]