Abstract
A type of hysteresis, similar to that observed in the heat capacity measurements (Openshaw et al., 1979), has been found in the room temperature unit cell parameters of a microcline sample 71104 and likewise indicates the existence of two forms of this microcline. The A-form (obtained on cooling the sample to approximately 80 K) has significantly different values of b, β and V to the B-form which is the more stable form above 300±10 K. The transition from the A- to the B-form occurs over a period of months and has an associated ΔV of −0.0011 nm3.
The cell parameters of the B-form have been measured up to 1278 K and show significant changes: a and V increase, b constracts, and c is unchanged on increasing temperature. The calculated thermal expansion ellipsoid is nearly uniaxial and similar in shape to that for sanidine. Below room temperature the isobaric thermal expansion coefficent αp, for a natural microcline is nearly four times as large as that for sanidine. Above room temperature αp for 71104 microcline decreases markedly with increasing temperature. This implies a rapid change in the thermal expansion behavior of microcline which has been correlated with the proposed phase transition.
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Borg, I.Y., Smith, D.K.: Calculated X-ray powder patterns for silicate minerals. Geol. Soc. Am. Mem. 122 (1966)
Burnham, C.W.: Lattice constant refinement. Carnegie Inst. Washington Yearb. 61, 132–135 (1962)
Grove, T.L., Hazen, R.M.: Alkali feldspar unit-cell parameters at liquid nitrogen temperatures: low temperature limits of the displacive transformation. Am. Mineral. 59, 1327–1329 (1974)
Grundy, H.D., Brown, W.L.: Preliminary single-crystal study of the lattice angles of triclinic feldspars at temperatures up to 1200° C Schweiz. Mineral. Petrogr. Mitt. 47, 21–30 (1967)
Henderson, C.M.B.: An elevated temperature X-ray study of synthetic disordered Na-Kalkali feldspars. Contrib. Mineral. Petrol. 70, 71–79 (1979)
Henderson, C.M.B., Taylor, D.: Thermal expansion of nitrides and oxynitrides of silica in relation to their structures. Trans. J. Brit. Ceram. Soc. 74, 49–53 (1975)
Holm, J.L., Kleppa, O.T.: Thermodynamics of the disordering process in albite. Am. Mineral. 53, 123–133 (1968)
Hovis, G.L., Peckins, E.: A new X-ray investigation of maximum microcline crystalline solutions. Contrib. Mineral. Petrol. 66, 345–349 (1978)
Hubbard, C.R., Swanson, H.E., Mauer, F.A.: A silicon powder diffraction standard reference material. J. Appl. Cryst. 8, 45–48 (1975)
Openshaw, R.E.: The low temperature heat capacities of analbite, low albite, microcline and sanidine. Princeton N.J.: PhD Dissertation, Princeton University, 1975
Openshaw, R.E., Hemingway, B.S., Robie, R.A., Krupka, K.M.: A room-temperature phase transition in microcline. Heat capacity measurements. 5, 83–93 (1979)
Orville, P.M.: Unit-cell parameters of the microcline-low albite and the sanidine-high albite solid solution series. Am. Mineral. 52, 55–86 (1967)
Prewitt, C.T., Sueno, S., Papike, J.J.: The crystal structures of high albite and monalbite at high temperatures. Am. Mineral. 61, 1213–1225 (1976)
Rosenholtz, J.L., Smith, D.T.: Linear thermal expansion of adularia. Am. Mineral. 26, 391–394 (1941)
Rosenholtz, J.L., Smith, D.T.: Thermal studies of orthoclase and microcline Am. Mineral. 27, 344–349 (1942)
Stewart, D.B.: Lattice parameters, composition, and Al/Si order in alkali felspars. In: Mineralogical Society of America Short Course Notes, Ribbe, P.H. (ed.). Blackburg, Virginia: Southern Printing Company 1975, pp. ST-1–ST-22
Stewart, D.B., Wright, T.L.: Al/Si order and symmetry of natural alkali feldspars, and the relationship of strained cell parameters to bulk composition. Bull. Soc. Franc. Minéral. Crist. 97, 356–377 (1974)
Waldbaum, D.R., Robie, R.A.: Calorimetric investigation of Na-K mixing and polymorphism in the alkali feldspars. Z. Krist. 134, 381–420 (1971)
Willaime, C., Brown, W.L., Perucaud, M.C.: On the orientation of thermal and compositional strain ellipsoids in feldspars. Am. Mineral. 59, 457–464 (1974)
Winter, J.K., Ghose, S., Okamura, F.P.: A high-temperature study of the thermal expansion and the anisotropy of the sodium atom in low albite. Am. Mineral. 62, 921–931 (1977)
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Openshaw, R.E., Henderson, C.M.B. & Brown, W.L. A room-temperature phase transition in maximum microcline. Phys Chem Minerals 5, 95–104 (1979). https://doi.org/10.1007/BF00308171
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DOI: https://doi.org/10.1007/BF00308171