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Humite End-Members

Humite Group (Mg,Fe) 2x+1 (SiO 4 ) x (F,OH) 2 where x = 1 (norbergite), 2 (chondrodite), 3 (humite), and 4 (clinohumite). In natural samples Mg>>FE and F>>OH. Humite End-Members. Magnesium-flourine end-members Norbergite Mg 2 SiO 4 ·MgF 2 Chondrodite 2Mg 2 SiO 4 ·MgF 2

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Humite End-Members

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  1. Humite Group(Mg,Fe)2x+1(SiO4)x(F,OH)2where x = 1 (norbergite), 2 (chondrodite), 3 (humite), and 4 (clinohumite).In natural samples Mg>>FE and F>>OH.

  2. Humite End-Members Magnesium-flourine end-members Norbergite Mg2SiO4·MgF2 Chondrodite 2Mg2SiO4·MgF2 Humite 3Mg2SiO4·MgF2 Clinohumite 4Mg2SiO4·MgF2 (Forsterite) Mg2SiO4 Magnesium-hydroxyl end-members Hydroxyl-chondrodite 2Mg2SiO4·Mg(OH)2 Hydroxyl-clinohumite 4Mg2SiO4·Mg(OH)2 Manganese-hydroxyl isotypes MAN Mn2SiO4·Mn(OH)2 Alleghanyite 2Mn2SiO4·Mn(OH)2 (Tephroite) Mn2SiO4

  3. Humite Occurrences The principal occurrence is in high grade metamorphosed mafic and ultramafic rocks. They have been found in Monte Somma, Mount Vesuvius, Italy; Paragas, Finland; Varmland, Sweden; Tilly Foster Mine, Brewster, New York, USA and some other localities. At one time, humites generated interest as a possible mineralogical site for water in the earths upper mantle. Titaniferous clinohumite was studied by Merrill et al. (1972) and was found to be stable as a hydrous mineral up to 1170°C at 3 GPa. Striated, brown, tabular crystals of Humite. Monte Somma (Vesuvius), Campania, Italy.Photomicrograph by Lou Perloff / Photo-Atlas of Minerals

  4. Humite Structure End-Member Norbergite Chondrodite Humite Clinohumite Formula (Mg,Fe)3SiO4(F,OH)2 (Mg,Fe)5(SiO4)2(F,OH)2 (Mg,Fe)7(SiO4)3(F,OH)2 (Mg,Fe)9(SiO4)4(F,OH)2 Form.Wt. 203.016 341.73 482.44 640.49 Z 4 2 4 2 Crystal System Orth Mono Orth Mono Point Group mmm 2/m mmm 2/m Space Group Pbnm P21/b Pbnm P21/b Unit Cell a(Å) 4.7104 4.7284 4.7408 4.7441 b(Å) 10.2718 10.2539 10.2580 10.2501 c(Å) 8.7476 7.7404 20.8526 13.6635  109.059 100.786 Vol(Å3) 423.25 359.30 1014.09 652.68 MolarVol 63.73 108.20 152.70 196.55 Density 3.186 3.158 3.159 3.258

  5. Humite Structure

  6. Humite Chemistry Octahedral Sites In the M sites, Ca substitutes up to .2 weight % CaO. Zn is also as abundent but is found more often in the Mn-isotypes. NiO as also been found in these sites. Ti is found to prefer the M3 site. Fe is also found to substitute for Mg. Tetrahedral Sites B and Be can substitute for Si.

  7. Humite Compressibility

  8. Humite Compressibility TF chondrodite (XOH = 0.42): A bulk modulus of K0,T=117.0(4) GPa was derived from P-V data with a pressure derivative of KT´=5.6(1). Previous compression studies of chondrodites revealed: K0,T=115.5(6) GPa, KT´=5.0(2), XOH=1.0, [1]; KS=118.4(1.6) GPa, XOH=0.68, [2]; K0,T=136(9) GPa, KT´=3.7(0.4), XOH=0.27, [3]; if KT´=4.9-5.5: K0,T=118-125. KiL clinohumite (XOH = 0.40): K0.T=119(3) GPa, KT´=6.3(8). If K´=5: K0.T=123.6(8) GPa. Previous compression studies of clinohumites revealed: K0.T=119.4(7) GPa, K´=4.8(2), XOH=1.0 [1]; KS=125(2) GPa, XOH = 0.71, [4]. These data suggest that chondrodite and clinohumite become less compressible with increasing F content. From http://www.louisville.edu/~galage01/hpc.pdf, Compression and pressure-dependent structural studies of F-bearing chondrodite and clinohumite Alexandra Friedrich1, George A. Lager2, Martin Kunz1, Peter Ulmer1, William G. Marshall3

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