Andrew Christy - Academia.edu (original) (raw)
Papers by Andrew Christy
Elements
The mineralogy of carbonatites reflects both the diversity of the sources of their parent magmas ... more The mineralogy of carbonatites reflects both the diversity of the sources of their parent magmas and their unusual chemistry. Carbonatites contain diverse suites of both primary magmatic minerals and later hydrothermal products. We present a summary of the variety of minerals found in carbon-atites, and note the economic importance of some of them, particularly those that are major sources of “critical elements”, such as Nb and rare earth elements (REEs), which are essential for modern technological applications. Selected mineral groups are then discussed in detail: the REE carbonates, the alkali-rich ephemeral minerals that are rarely preserved but that may be important in the petrogenesis of carbonatites and their metasomatic haloes in adjacent rocks, and the Nb-rich oxides of the pyrochlore supergroup.
Proc. Indon Petrol. Assoc., 34th Ann. Conv.
The Canadian Mineralogist, 2019
Gaildunningite, ideally Hg-3(2+)[NHg22+](18)(Cl,I)(24), is a new mineral from the Clear Creek min... more Gaildunningite, ideally Hg-3(2+)[NHg22+](18)(Cl,I)(24), is a new mineral from the Clear Creek mine, New Idria mining district, San Benito County, California, USA. It is orthorhombic, space group Amam, Z 1/4 4; a 26.381(6), b 45.590(10), c 6.6840(15) angstrom, V 8039(5) angstrom(3). Chemical analysis by electron microprobe gave Hg 76.87, I 12.55, Cl 3.79, Br 0.56, S 0.18 wt.%; N 2.45, O 0.28, and H 0.02 wt.% were derived from the crystal structure to give a total of 96.70 wt.%. The empirical formulae (calculated on the basis of 39.44 Hg with 18 N and OH added to give electroneutrality) is Hg39.442+N18[Cl11.00I10.18(OH)(1.81)Br0.73S0.58](Sigma 24.30) and the simplified formula is Hg-3(2+)[NHg22+](18)(Cl,I)(24). The seven strongest lines in the X-ray powder diffraction pattern [listed as d (angstrom), I, (hkl)] are as follows: 2.853, 100, (880, 0.16.0); 2.776, 100, (462, 5.14.0); 2.745, 100, (542); 5.717, 50, (440, 080); 5.965, 40, (131); 5.018, 40, (331); 1.673, 40, (004). Gaildunningite generally forms complex parallel intergrowths of fibrous to acicular crystals elongated along [001]. Acicular yellow to orange to darker orange-red crystals up to 0.1 mm long form matted nests lining vugs within white-grey quartz. Gaildunningite has a vitreous to adamantine luster, is transparent, and does not fluoresce under short-or long-wave ultraviolet light. Mohs hardness approximate to 3 and the calculated density is 8.22 g/cm(3). It is brittle with an uneven fracture and has very good cleavage on {100} and {010} and good cleavage on {001}; neither parting nor twinning was observed. It is grey in reflected light with possibly minor bireflectance but no reflectance pleochroism, and strong yellow-orange internal reflections are evident even in plane-polarized light. The Raman spectrum indicates the presence of Hg-N bonds in the structure. The crystal structure of gaildunningite is based on a well-ordered three-dimensional [NHg2](+) net of near-linear N-Hg-N groups, where each N3- is tetrahedrally coordinated by Hg2+. The net is comprised of two five-membered, three six-membered, one seven-membered, and one eight-membered rings of N-Hg-N groups. The interstitial part of the structure is significantly disordered and consists of (Hg2+) and (I-, Cl-, Br-, S2-, OH-) ions. A new bond-valence parameter has been derived for (Hg2+-N3-) bonds: R-o = 1.964 angstrom, b 1/4 0.37; this gives bond-valence sums at the N3- ions in accord with the valence-sum rule.Gaildunningite and unnamed CCUK-18 are the only (Hg-N-I)-bearing minerals discovered at Clear Creek to date and are closely associated; gaildunningite is the later of these two minerals and tends to grow on CCUK-18. They post-date the iodine-free nitride mosesite and the (N, I)-free chlorides such as eglestonite, implying that iodine was a late addition to the overall chemical system. Both the mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2018-029). The mineral is named after Gail E. Dunning (b. 1937), a prominent field-collector of minerals from the New Idria mining district who has been responsible for the discovery of many new mercury-bearing minerals.
Mineralogical Magazine, 2017
Four specimens of the roméite-group minerals oxyplumboroméite and fluorcalcioroméite from the Lån... more Four specimens of the roméite-group minerals oxyplumboroméite and fluorcalcioroméite from the Långban Mn-Fe deposit in Central Sweden were structurally and chemically characterized by single-crystal X-ray diffraction, electron microprobe analysis and infrared spectroscopy. The data obtained and those on additional roméite samples from literature show that the main structural variations within the roméite group are related to variations in the content of Pb2+, which is incorporated into the roméite structure via the substitution Pb2+→A2+ where A2+ = Ca, Mn and Sr. Additionally, the cation occupancy at the six-fold coordinated B site, which is associated with the heterovalent substitution BFe3+ + Y☐→BSb5++YO2-, can strongly affect structural parameters.Chemical formulae of the roméite minerals group are discussed. According to crystal-chemical information, the species associated with the name ‘kenoplumboroméite’, hydroxycalcioroméite and fluorcalcioroméite most closely approximate end...
Journal of Asian Earth Sciences, 2018
European Journal of Mineralogy, 2016
The type specimen of partzite has been reinvestigated by powder X-ray diffraction and electron mi... more The type specimen of partzite has been reinvestigated by powder X-ray diffraction and electron microprobe traverses. Re-examination of the type material shows that it is a mixture of several phases, intergrown on a submicrometre scale and hence not fully resolved by electron microprobe. Investigation of major-element spot analyses for correlations between elements indicates that the two dominant phases are a plumboromeite-like oxide phase and a chrysocolla-like amorphous Cu silicate. This analysis also suggested the presence of several minor phases that were too scarce to be detectable by X-ray diffraction, including acanthite, chlorargyrite, baryte, halite, and an Al-rich clay mineral. Lack of correlation between Si-corrected Cu content and Sb content implies that Cu is not a significant component of the romeite-group mineral. Partzite is therefore discredited as a valid mineral species. This proposal has been approved by the IMA CNMNC (proposal 16-B).
European Journal of Mineralogy, 2017
Physics and Chemistry of Minerals, 2005
Physics and Chemistry of Minerals, 1989
physica status solidi (b), 2006
ABSTRACT The 13C NMR spectra of a carbon nanofoam sample, exhibiting a peak in the ZFC magnetic s... more ABSTRACT The 13C NMR spectra of a carbon nanofoam sample, exhibiting a peak in the ZFC magnetic susceptibility, show a single 13C line at room temperature and a two peak structure at 100 K. The splitting and the NMR shifts are however much too small to be associated with true ferromagnetism as for instance observed in TDAE-C60 below TC. The X-band EPR spectra show the presence of a least three different paramagnetic clusters with ga = 2.0016, gb = 2.0031, gc = 2.0036 and very different electronic spin–lattice relaxation times. In some samples the CW EPR spectra show an additional rather broad and strongly temperature dependent line shifted to lower fields, which is characteristic of ferromagnetic systems. The results thus show an inhomogeneous super-paramagnetic or spin-glass like nature of magnetism in cluster assembled carbon nanofoam rather than homogeneous ferromagnetism. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Journal of Solid State Chemistry, 2007
Mineralogical Magazine, 2016
A crystallographic and chemical study of two 'elsmoreite' samples (previously described a... more A crystallographic and chemical study of two 'elsmoreite' samples (previously described as 'ferritungstite') from the Hemerdon mine (now known as the Drakelands mine), Devon, United Kingdom has shown them to be two different polytypes of hydrokenoelsmoreite. Hydrokenoelsmoreite-3C(HKE-3C) crystallizes in space group , with the unit-cell parameter a = 10.3065(3) Å. Hydrokenoelsmoreite-6R (HKE-6R) crystallizes in space group , with the unit-cell parameters a = 7.2882(2) Å and c = 35.7056(14)Å. Chemical analyses showed that both polytypes have Na and Fe/Al substitution giving the formulae: (Na0.28Ca0.04K0.02(H2O)0.20⁏1.46)∑2.00(W1.47Fe3+0.32Al0.21As5+0.01)∑2.00[O4.79(OH)1.21]∑6.00·(H2O)(3C) and (Na0.24Ca0.04K0.03(H2O)0.63⁏1.06)∑2.00(W1.42Fe3+0.49Al0.08As5+0.01)∑2.00[O4.65(OH)1.35]∑6.00·(H2O)(6R). The doubling of the unit cell in the 6R phase is due to ordering of Na and ( ,H2O) in the A site; no long-range ordering is observed between W and Fe/Al in the B site.
Geological Society of America Abstracts with Programs
Encyclopedia of Earth Sciences Series, 2017
Water Science and Technology, 2005
This study aimed to establish if there is any evidence that soil mineralogical and/or chemical co... more This study aimed to establish if there is any evidence that soil mineralogical and/or chemical composition influence the composition and quality of wine grapes. In the initial phase of the study, soils and grapes were sampled in two riesling vineyards in South Australia. Soils were analysed for a wide range of total major and trace elements; soil cation extracts and grape juices were analysed for 27 trace elements by ICP-MS and ICP-AES. The results show that grape juice properties such as Baumé and titratable acidity (TA) are clearly correlated with several plant-available trace elements in the soil. Most notable of these are Ca, Sr, Ba, Pb and Si. Soil clay content also plays a (lesser) role. The cations Ca, Sr, Ba and Pb are closely similar to one another in their relationships to Baumé and TA, strongly indicating that the correlations are real. It is evident from our results that soil cation chemistry does indeed have an influence on wine grape composition. Such knowledge has the...
Mineralogical Magazine, 2016
Relative to its extremely low abundance in the Earth's crust, tellurium is the most mineralog... more Relative to its extremely low abundance in the Earth's crust, tellurium is the most mineralogically diverse chemical element, with over 160 mineral species known that contain essential Te, many of them with unique crystal structures. We review the crystal structures of 703 tellurium oxysalts for which good refinements exist, including 55 that are known to occur as minerals. The dataset is restricted to compounds where oxygen is the only ligand that is strongly bound to Te, but most of the Periodic Table is represented in the compounds that are reviewed. The dataset contains 375 structures that contain only Te4+ cations and 302 with only Te6+, with 26 of the compounds containing Te in both valence states. Te6+ was almost exclusively in rather regular octahedral coordination by oxygen ligands, with only two instances each of 4- and 5-coordination. Conversely, the lone-pair cation Te4+ displayed irregular coordination, with a broad range of coordination numbers and bond distances. ...
Acta crystallographica Section B, Structural science, crystal engineering and materials, 2017
A new superstructure of the mineral camerolaite, Cu6Al3(OH)18(H2O)2[Sb(OH)6](SO4), has been refin... more A new superstructure of the mineral camerolaite, Cu6Al3(OH)18(H2O)2[Sb(OH)6](SO4), has been refined in space group P\bar 1 with unit-cell parameters aP = 7.7660 (16), bP = 8.759 (4), cP = 11.306 (2) Å, αP = 108.67 (4), βP = 83.41 (3), γP = 126.64 (2)°, V = 581.6 (3) Å(3) and Z = 1, with R1 = 0.0951 (all data). This is the first refined example of a cyanotrichite-group mineral in which long-range order of interlayer anions produces a superstructure along b, although diffuse scattering has previously been reported that corresponds to short-range order. Though the structure shares with other members of the cyanotrichite group a structural unit in which ribbons of edge-sharing Cu and Al octahedra form layers || (001), the superstructure arises from regular alternation of [SO4] and [Sb(OH)6] polyhedra along rods that lie between the layers, and phase coupling between rods that maximizes the distance between [SO4] groups of adjacent rods along a and c directions. This arrangement suggests...
American Mineralogist, 2002
Elements
The mineralogy of carbonatites reflects both the diversity of the sources of their parent magmas ... more The mineralogy of carbonatites reflects both the diversity of the sources of their parent magmas and their unusual chemistry. Carbonatites contain diverse suites of both primary magmatic minerals and later hydrothermal products. We present a summary of the variety of minerals found in carbon-atites, and note the economic importance of some of them, particularly those that are major sources of “critical elements”, such as Nb and rare earth elements (REEs), which are essential for modern technological applications. Selected mineral groups are then discussed in detail: the REE carbonates, the alkali-rich ephemeral minerals that are rarely preserved but that may be important in the petrogenesis of carbonatites and their metasomatic haloes in adjacent rocks, and the Nb-rich oxides of the pyrochlore supergroup.
Proc. Indon Petrol. Assoc., 34th Ann. Conv.
The Canadian Mineralogist, 2019
Gaildunningite, ideally Hg-3(2+)[NHg22+](18)(Cl,I)(24), is a new mineral from the Clear Creek min... more Gaildunningite, ideally Hg-3(2+)[NHg22+](18)(Cl,I)(24), is a new mineral from the Clear Creek mine, New Idria mining district, San Benito County, California, USA. It is orthorhombic, space group Amam, Z 1/4 4; a 26.381(6), b 45.590(10), c 6.6840(15) angstrom, V 8039(5) angstrom(3). Chemical analysis by electron microprobe gave Hg 76.87, I 12.55, Cl 3.79, Br 0.56, S 0.18 wt.%; N 2.45, O 0.28, and H 0.02 wt.% were derived from the crystal structure to give a total of 96.70 wt.%. The empirical formulae (calculated on the basis of 39.44 Hg with 18 N and OH added to give electroneutrality) is Hg39.442+N18[Cl11.00I10.18(OH)(1.81)Br0.73S0.58](Sigma 24.30) and the simplified formula is Hg-3(2+)[NHg22+](18)(Cl,I)(24). The seven strongest lines in the X-ray powder diffraction pattern [listed as d (angstrom), I, (hkl)] are as follows: 2.853, 100, (880, 0.16.0); 2.776, 100, (462, 5.14.0); 2.745, 100, (542); 5.717, 50, (440, 080); 5.965, 40, (131); 5.018, 40, (331); 1.673, 40, (004). Gaildunningite generally forms complex parallel intergrowths of fibrous to acicular crystals elongated along [001]. Acicular yellow to orange to darker orange-red crystals up to 0.1 mm long form matted nests lining vugs within white-grey quartz. Gaildunningite has a vitreous to adamantine luster, is transparent, and does not fluoresce under short-or long-wave ultraviolet light. Mohs hardness approximate to 3 and the calculated density is 8.22 g/cm(3). It is brittle with an uneven fracture and has very good cleavage on {100} and {010} and good cleavage on {001}; neither parting nor twinning was observed. It is grey in reflected light with possibly minor bireflectance but no reflectance pleochroism, and strong yellow-orange internal reflections are evident even in plane-polarized light. The Raman spectrum indicates the presence of Hg-N bonds in the structure. The crystal structure of gaildunningite is based on a well-ordered three-dimensional [NHg2](+) net of near-linear N-Hg-N groups, where each N3- is tetrahedrally coordinated by Hg2+. The net is comprised of two five-membered, three six-membered, one seven-membered, and one eight-membered rings of N-Hg-N groups. The interstitial part of the structure is significantly disordered and consists of (Hg2+) and (I-, Cl-, Br-, S2-, OH-) ions. A new bond-valence parameter has been derived for (Hg2+-N3-) bonds: R-o = 1.964 angstrom, b 1/4 0.37; this gives bond-valence sums at the N3- ions in accord with the valence-sum rule.Gaildunningite and unnamed CCUK-18 are the only (Hg-N-I)-bearing minerals discovered at Clear Creek to date and are closely associated; gaildunningite is the later of these two minerals and tends to grow on CCUK-18. They post-date the iodine-free nitride mosesite and the (N, I)-free chlorides such as eglestonite, implying that iodine was a late addition to the overall chemical system. Both the mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2018-029). The mineral is named after Gail E. Dunning (b. 1937), a prominent field-collector of minerals from the New Idria mining district who has been responsible for the discovery of many new mercury-bearing minerals.
Mineralogical Magazine, 2017
Four specimens of the roméite-group minerals oxyplumboroméite and fluorcalcioroméite from the Lån... more Four specimens of the roméite-group minerals oxyplumboroméite and fluorcalcioroméite from the Långban Mn-Fe deposit in Central Sweden were structurally and chemically characterized by single-crystal X-ray diffraction, electron microprobe analysis and infrared spectroscopy. The data obtained and those on additional roméite samples from literature show that the main structural variations within the roméite group are related to variations in the content of Pb2+, which is incorporated into the roméite structure via the substitution Pb2+→A2+ where A2+ = Ca, Mn and Sr. Additionally, the cation occupancy at the six-fold coordinated B site, which is associated with the heterovalent substitution BFe3+ + Y☐→BSb5++YO2-, can strongly affect structural parameters.Chemical formulae of the roméite minerals group are discussed. According to crystal-chemical information, the species associated with the name ‘kenoplumboroméite’, hydroxycalcioroméite and fluorcalcioroméite most closely approximate end...
Journal of Asian Earth Sciences, 2018
European Journal of Mineralogy, 2016
The type specimen of partzite has been reinvestigated by powder X-ray diffraction and electron mi... more The type specimen of partzite has been reinvestigated by powder X-ray diffraction and electron microprobe traverses. Re-examination of the type material shows that it is a mixture of several phases, intergrown on a submicrometre scale and hence not fully resolved by electron microprobe. Investigation of major-element spot analyses for correlations between elements indicates that the two dominant phases are a plumboromeite-like oxide phase and a chrysocolla-like amorphous Cu silicate. This analysis also suggested the presence of several minor phases that were too scarce to be detectable by X-ray diffraction, including acanthite, chlorargyrite, baryte, halite, and an Al-rich clay mineral. Lack of correlation between Si-corrected Cu content and Sb content implies that Cu is not a significant component of the romeite-group mineral. Partzite is therefore discredited as a valid mineral species. This proposal has been approved by the IMA CNMNC (proposal 16-B).
European Journal of Mineralogy, 2017
Physics and Chemistry of Minerals, 2005
Physics and Chemistry of Minerals, 1989
physica status solidi (b), 2006
ABSTRACT The 13C NMR spectra of a carbon nanofoam sample, exhibiting a peak in the ZFC magnetic s... more ABSTRACT The 13C NMR spectra of a carbon nanofoam sample, exhibiting a peak in the ZFC magnetic susceptibility, show a single 13C line at room temperature and a two peak structure at 100 K. The splitting and the NMR shifts are however much too small to be associated with true ferromagnetism as for instance observed in TDAE-C60 below TC. The X-band EPR spectra show the presence of a least three different paramagnetic clusters with ga = 2.0016, gb = 2.0031, gc = 2.0036 and very different electronic spin–lattice relaxation times. In some samples the CW EPR spectra show an additional rather broad and strongly temperature dependent line shifted to lower fields, which is characteristic of ferromagnetic systems. The results thus show an inhomogeneous super-paramagnetic or spin-glass like nature of magnetism in cluster assembled carbon nanofoam rather than homogeneous ferromagnetism. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Journal of Solid State Chemistry, 2007
Mineralogical Magazine, 2016
A crystallographic and chemical study of two 'elsmoreite' samples (previously described a... more A crystallographic and chemical study of two 'elsmoreite' samples (previously described as 'ferritungstite') from the Hemerdon mine (now known as the Drakelands mine), Devon, United Kingdom has shown them to be two different polytypes of hydrokenoelsmoreite. Hydrokenoelsmoreite-3C(HKE-3C) crystallizes in space group , with the unit-cell parameter a = 10.3065(3) Å. Hydrokenoelsmoreite-6R (HKE-6R) crystallizes in space group , with the unit-cell parameters a = 7.2882(2) Å and c = 35.7056(14)Å. Chemical analyses showed that both polytypes have Na and Fe/Al substitution giving the formulae: (Na0.28Ca0.04K0.02(H2O)0.20⁏1.46)∑2.00(W1.47Fe3+0.32Al0.21As5+0.01)∑2.00[O4.79(OH)1.21]∑6.00·(H2O)(3C) and (Na0.24Ca0.04K0.03(H2O)0.63⁏1.06)∑2.00(W1.42Fe3+0.49Al0.08As5+0.01)∑2.00[O4.65(OH)1.35]∑6.00·(H2O)(6R). The doubling of the unit cell in the 6R phase is due to ordering of Na and ( ,H2O) in the A site; no long-range ordering is observed between W and Fe/Al in the B site.
Geological Society of America Abstracts with Programs
Encyclopedia of Earth Sciences Series, 2017
Water Science and Technology, 2005
This study aimed to establish if there is any evidence that soil mineralogical and/or chemical co... more This study aimed to establish if there is any evidence that soil mineralogical and/or chemical composition influence the composition and quality of wine grapes. In the initial phase of the study, soils and grapes were sampled in two riesling vineyards in South Australia. Soils were analysed for a wide range of total major and trace elements; soil cation extracts and grape juices were analysed for 27 trace elements by ICP-MS and ICP-AES. The results show that grape juice properties such as Baumé and titratable acidity (TA) are clearly correlated with several plant-available trace elements in the soil. Most notable of these are Ca, Sr, Ba, Pb and Si. Soil clay content also plays a (lesser) role. The cations Ca, Sr, Ba and Pb are closely similar to one another in their relationships to Baumé and TA, strongly indicating that the correlations are real. It is evident from our results that soil cation chemistry does indeed have an influence on wine grape composition. Such knowledge has the...
Mineralogical Magazine, 2016
Relative to its extremely low abundance in the Earth's crust, tellurium is the most mineralog... more Relative to its extremely low abundance in the Earth's crust, tellurium is the most mineralogically diverse chemical element, with over 160 mineral species known that contain essential Te, many of them with unique crystal structures. We review the crystal structures of 703 tellurium oxysalts for which good refinements exist, including 55 that are known to occur as minerals. The dataset is restricted to compounds where oxygen is the only ligand that is strongly bound to Te, but most of the Periodic Table is represented in the compounds that are reviewed. The dataset contains 375 structures that contain only Te4+ cations and 302 with only Te6+, with 26 of the compounds containing Te in both valence states. Te6+ was almost exclusively in rather regular octahedral coordination by oxygen ligands, with only two instances each of 4- and 5-coordination. Conversely, the lone-pair cation Te4+ displayed irregular coordination, with a broad range of coordination numbers and bond distances. ...
Acta crystallographica Section B, Structural science, crystal engineering and materials, 2017
A new superstructure of the mineral camerolaite, Cu6Al3(OH)18(H2O)2[Sb(OH)6](SO4), has been refin... more A new superstructure of the mineral camerolaite, Cu6Al3(OH)18(H2O)2[Sb(OH)6](SO4), has been refined in space group P\bar 1 with unit-cell parameters aP = 7.7660 (16), bP = 8.759 (4), cP = 11.306 (2) Å, αP = 108.67 (4), βP = 83.41 (3), γP = 126.64 (2)°, V = 581.6 (3) Å(3) and Z = 1, with R1 = 0.0951 (all data). This is the first refined example of a cyanotrichite-group mineral in which long-range order of interlayer anions produces a superstructure along b, although diffuse scattering has previously been reported that corresponds to short-range order. Though the structure shares with other members of the cyanotrichite group a structural unit in which ribbons of edge-sharing Cu and Al octahedra form layers || (001), the superstructure arises from regular alternation of [SO4] and [Sb(OH)6] polyhedra along rods that lie between the layers, and phase coupling between rods that maximizes the distance between [SO4] groups of adjacent rods along a and c directions. This arrangement suggests...
American Mineralogist, 2002