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Papers by Michele van Panhuys-Sigler
Scottish Journal of Geology, Dec 1, 1990
Synopsis Permian sandstones from the Cock of Arran area contain small amounts of sphene cement. T... more Synopsis Permian sandstones from the Cock of Arran area contain small amounts of sphene cement. The sphene occurs as a minor phase (up to 2%) in small patches cementing several grains, and as individual crystals with well developed crystal faces grown into pore space ...
Bulletin de minéralogie (Paris), 1981
On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These... more On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These are <001>, <100>, <010>, <110>, <10[-2]>, <102>, <11[-2]>, <112>, <012> and <011>. Using a broken bond model the attachment energies can be calculated and so the F faces (containing two or more PBCs) can be classified in the order of decreasing importance. In the case of free atoms in the crystallizing phase one obtains : {110}, {010}, {100}, {111}, {[-2]21}, {111}, {021}, {001}, {221} and {011}. The results are identical for the other monoclinic pyroxenes : hedenbergite, augite, jadeite and acmite. Drawings of the theoretical growth form of the crystals are given assuming the attachment energy to be proportional to the growth rate of a face. When the eventual presence of Si?O? groups in the crystallizing phase is considered as an external factor, the growth form, as far as it depends on the crystal structure is the one calculated on the basis of free atoms. Diopside, hedenbergite and augite are bound by {110}, {010}, {[-1]11}, {111} and jadeite and acmite by {110} and {[-1]11}. It is questionable whether the various forms appearing in nature are always due to external factors or whether the hypothesis that EaH is directly proportional to the growth rate is justified.
Scottish Journal of Geology, Nov 1, 1996
Synopsis Roscoelite, a vanadium mica, occurs in the cores of reduction spots within the Lower Old... more Synopsis Roscoelite, a vanadium mica, occurs in the cores of reduction spots within the Lower Old Red Sandstone that crops out in Gamrie Bay (Moray Firth). The finely crystallized mineral is seen both as a cement in the sandstone and replacing plagioclase feldspar in a lithic ...
Bulletin de Minéralogie, 1981
On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These... more On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These are <001>, <100>, <010>, <110>, <10[-2]>, <102>, <11[-2]>, <112>, <012> and <011>. Using a broken bond model the attachment energies can be calculated and so the F faces (containing two or more PBCs) can be classified in the order of decreasing importance. In the case of free atoms in the crystallizing phase one obtains : {110}, {010}, {100}, {111}, {[-2]21}, {111}, {021}, {001}, {221} and {011}. The results are identical for the other monoclinic pyroxenes : hedenbergite, augite, jadeite and acmite. Drawings of the theoretical growth form of the crystals are given assuming the attachment energy to be proportional to the growth rate of a face. When the eventual presence of Si?O? groups in the crystallizing phase is considered as an external factor, the growth form, as far as it depends on the crystal structure is the one calcula...
Journal of crystal growth, 1987
Crystallization of lead chloride, PbC12, from pure aqueous solution produces crystals with domina... more Crystallization of lead chloride, PbC12, from pure aqueous solution produces crystals with dominant (211) and smaller (010) and (100) faces at low supersaturation. Increase of supersaturation yields crystals elongated along the c axis. Growth from a previously prepared saturated solution gives crystals elongated along the c axis with (011) as main terminal faces. This habit also occurs when KC1, NH4C1 or CdC12 or mixtures of these are added to a freshly prepared supersaturated solution. Only at low additive concentration and at low supersaturation (211) is dominant. The latter habit is supposed to be caused by adsorption of OH-ions on (211). A deposit of Pb(OH)Cl has been observed. Crystallization from HCI containing solutions enhances the (010) and (121) forms, presumably through preferred adsorption of H~and possibly PbCl~ions. Increasing supersaturation diminishes the effect of the habit modifying process until the stage where dendrites appear.
On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These... more On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These are <001>, <100>, <010>, <110>, <10[-2]>, <102>, <11[-2]>, <112>, <012> and <011>. Using a broken bond model the attachment energies can be calculated and so the F faces (containing two or more PBCs) can be classified in the order of decreasing importance. In the case of free atoms in the crystallizing phase one obtains : {110}, {010}, {100}, {111}, {[-2]21}, {111}, {021}, {001}, {221} and {011}. The results are identical for the other monoclinic pyroxenes : hedenbergite, augite, jadeite and acmite. Drawings of the theoretical growth form of the crystals are given assuming the attachment energy to be proportional to the growth rate of a face. When the eventual presence of Si?O? groups in the crystallizing phase is considered as an external factor, the growth form, as far as it depends on the crystal structure is the one calculated on the basis of free atoms. Diopside, hedenbergite and augite are bound by {110}, {010}, {[-1]11}, {111} and jadeite and acmite by {110} and {[-1]11}. It is questionable whether the various forms appearing in nature are always due to external factors or whether the hypothesis that EaH is directly proportional to the growth rate is justified.
Scottish Journal of Geology, Dec 1, 1990
Synopsis Permian sandstones from the Cock of Arran area contain small amounts of sphene cement. T... more Synopsis Permian sandstones from the Cock of Arran area contain small amounts of sphene cement. The sphene occurs as a minor phase (up to 2%) in small patches cementing several grains, and as individual crystals with well developed crystal faces grown into pore space ...
Bulletin de minéralogie (Paris), 1981
On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These... more On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These are <001>, <100>, <010>, <110>, <10[-2]>, <102>, <11[-2]>, <112>, <012> and <011>. Using a broken bond model the attachment energies can be calculated and so the F faces (containing two or more PBCs) can be classified in the order of decreasing importance. In the case of free atoms in the crystallizing phase one obtains : {110}, {010}, {100}, {111}, {[-2]21}, {111}, {021}, {001}, {221} and {011}. The results are identical for the other monoclinic pyroxenes : hedenbergite, augite, jadeite and acmite. Drawings of the theoretical growth form of the crystals are given assuming the attachment energy to be proportional to the growth rate of a face. When the eventual presence of Si?O? groups in the crystallizing phase is considered as an external factor, the growth form, as far as it depends on the crystal structure is the one calculated on the basis of free atoms. Diopside, hedenbergite and augite are bound by {110}, {010}, {[-1]11}, {111} and jadeite and acmite by {110} and {[-1]11}. It is questionable whether the various forms appearing in nature are always due to external factors or whether the hypothesis that EaH is directly proportional to the growth rate is justified.
Scottish Journal of Geology, Nov 1, 1996
Synopsis Roscoelite, a vanadium mica, occurs in the cores of reduction spots within the Lower Old... more Synopsis Roscoelite, a vanadium mica, occurs in the cores of reduction spots within the Lower Old Red Sandstone that crops out in Gamrie Bay (Moray Firth). The finely crystallized mineral is seen both as a cement in the sandstone and replacing plagioclase feldspar in a lithic ...
Bulletin de Minéralogie, 1981
On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These... more On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These are <001>, <100>, <010>, <110>, <10[-2]>, <102>, <11[-2]>, <112>, <012> and <011>. Using a broken bond model the attachment energies can be calculated and so the F faces (containing two or more PBCs) can be classified in the order of decreasing importance. In the case of free atoms in the crystallizing phase one obtains : {110}, {010}, {100}, {111}, {[-2]21}, {111}, {021}, {001}, {221} and {011}. The results are identical for the other monoclinic pyroxenes : hedenbergite, augite, jadeite and acmite. Drawings of the theoretical growth form of the crystals are given assuming the attachment energy to be proportional to the growth rate of a face. When the eventual presence of Si?O? groups in the crystallizing phase is considered as an external factor, the growth form, as far as it depends on the crystal structure is the one calcula...
Journal of crystal growth, 1987
Crystallization of lead chloride, PbC12, from pure aqueous solution produces crystals with domina... more Crystallization of lead chloride, PbC12, from pure aqueous solution produces crystals with dominant (211) and smaller (010) and (100) faces at low supersaturation. Increase of supersaturation yields crystals elongated along the c axis. Growth from a previously prepared saturated solution gives crystals elongated along the c axis with (011) as main terminal faces. This habit also occurs when KC1, NH4C1 or CdC12 or mixtures of these are added to a freshly prepared supersaturated solution. Only at low additive concentration and at low supersaturation (211) is dominant. The latter habit is supposed to be caused by adsorption of OH-ions on (211). A deposit of Pb(OH)Cl has been observed. Crystallization from HCI containing solutions enhances the (010) and (121) forms, presumably through preferred adsorption of H~and possibly PbCl~ions. Increasing supersaturation diminishes the effect of the habit modifying process until the stage where dendrites appear.
On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These... more On computer-drawn projections of the structure of diopside (CaMgSi?O?) the PBCs are sought. These are <001>, <100>, <010>, <110>, <10[-2]>, <102>, <11[-2]>, <112>, <012> and <011>. Using a broken bond model the attachment energies can be calculated and so the F faces (containing two or more PBCs) can be classified in the order of decreasing importance. In the case of free atoms in the crystallizing phase one obtains : {110}, {010}, {100}, {111}, {[-2]21}, {111}, {021}, {001}, {221} and {011}. The results are identical for the other monoclinic pyroxenes : hedenbergite, augite, jadeite and acmite. Drawings of the theoretical growth form of the crystals are given assuming the attachment energy to be proportional to the growth rate of a face. When the eventual presence of Si?O? groups in the crystallizing phase is considered as an external factor, the growth form, as far as it depends on the crystal structure is the one calculated on the basis of free atoms. Diopside, hedenbergite and augite are bound by {110}, {010}, {[-1]11}, {111} and jadeite and acmite by {110} and {[-1]11}. It is questionable whether the various forms appearing in nature are always due to external factors or whether the hypothesis that EaH is directly proportional to the growth rate is justified.