• journal_title：Mineralogical Magazine
• Contributor：F. Nestola ; D. Pasqual ; M. D. Welch ; R. Oberti
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2012-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2012.076.4.14
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：76
• issue：4
• firstpage：987
• section：Articles

A single-crystal X-ray diffraction study of a sample of natural gedrite from North Carolina, USA, with the crystal-chemical formula ^ANa_0.47^B(Na_0.03Mg_0.97 Mn_0.02Ca_0.04)^C(Mg_3.52 Al_1.15 ) ^T(Si_6.31Al_1.69)O₂₂ ^W(OH)₂, up to a maximum pressure of 7 GPa, revealed the following bulk and axial moduli and their pressure derivatives: K_0T = 91.2(6) GPa [K_0T′ = 6.3(2)]; K_0T(a) = 60.5(6) GPa [K_0T(a)′ = 6.1(2)]; K_0T(b) = 122.8(2.6) GPa [K_0T(b)′ = 5.7(8)]; K_0T(c) = 119.7(1.5) GPa [K_0T(c)′ = 5.1(5)]. Gedrite has a much higher bulk modulus than anthophyllite (66 GPa) and proto-amphibole (64 GPa). All of the three axial moduli of gedrite are higher than those of these two other orthoamphiboles. The greater stiffness of gedrite along [100] is due to its high ^ANa content, which is almost zero in anthophyllite and proto-amphibole. The much greater stiffness parallel to the (100) plane of gedrite compared with the two other amphiboles is probably due to its high ^CAl content. A comparison is made with published data available for orthorhombic ^B(Mg,Mn,Fe) and monoclinic ^BCa amphiboles to identify correlations between crystal-chemistry and compressibility in amphiboles.