Papers by Stefano Merlino
Canadian Mineralogist, Jun 1, 2000
The crystal structure of normandite from Amdrup Fjord, Greenland and from Mont Saint-Hilaire, Que... more The crystal structure of normandite from Amdrup Fjord, Greenland and from Mont Saint-Hilaire, Quebec, was solved and refined to a residual R 1 of 0.033 and 0.047, respectively. Normandite is a member of the cuspidine group and, more precisely, the Ca-Ti-dominant analogue of låvenite. Consequently, its structure can be described in terms of "walls" of octahedra, interconnected by corner-sharing and through disilicate groups. These structural "modules" are arranged with the same topology as in cuspidine, hiortdahlite-II, janhaugite and niocalite. EPMA and SEM studies of the Amdrup Fjord material show distinct chemical zoning due to a wide variation of the major elements Na, Ca, Mn, Zr, and Ti, such that a "låvenitic" core gives way to a "normanditic" margin. From these data, the following ideal crystal-chemical formulae are derived: NaCaMnTiSi 2 O 7 OF for normandite and NaNaMZrSi 2 O 7 F 2 (M = Mn, Fe, Ca, Ti) for låvenite.
Canadian Mineralogist, 1988
The crystal structures of the minerals in the cuspidine wohlerite-11veni te group can be describ... more The crystal structures of the minerals in the cuspidine wohlerite-11veni te group can be described in terms of two kinds of modules whose connections form the structures of the various phases: "octahedral walls" four columns wide and running along c, and dionhosilicate groups. The octahedral walls are interconnected by comer sharing to create a framework that is the common feature in all the structures of the family. There are various ways to distrib ute the Si207 units, which serve to strengthen the frame work. Ten different structure-types v.:,ere derived 11 within fixed cell dimensions (a "' b "" 10.5 A, c "" 7.3 A). One of these structure-typeS, with topological symmetry P211a, is shown by cuspidine and llvenite, both with space-group symmetry P21/a, as well as by niocalite, in which the space-group symmetry is lowered to Pa by the ordering of the octahedral cations. Another structure-type, with topo logical symmetry P2 1, is shown by w...
Materials Today, 2004
1. Modular series - principles and types 2. Ordered derivative structures 3. Polytypes and polyty... more 1. Modular series - principles and types 2. Ordered derivative structures 3. Polytypes and polytype categories 4. Application of modularity to structure description and modelling 5. Modularity at crystal scale - twinning
Acta Crystallographica Section A Foundations of Crystallography, 1996
The Canadian Mineralogist, 2012
"Guarinite" is a typical accessory mineral of the Monte Somma syenite; it belongs to the cuspidin... more "Guarinite" is a typical accessory mineral of the Monte Somma syenite; it belongs to the cuspidine group and displays a domain structure. "Guarinite" contains up to three distinct domains, corresponding to three different ways to connect disilicate groups and walls of octahedra; these may all be simultaneously present in the same crystal. The domains present in the crystals of "guarinite" have cell type I, II and IV, according to the classification scheme proposed for cuspidine-group minerals. Domain IV is the most common, and domain I is the rarest; domain II may occur as the only domain, whereas domain I occurs only in association with domain IV, which invariably predominates. So far, the actual structure of the various domains had not been defined. EPMA and single-crystal structural studies indicate that domain I of "guarinite" displays space group P1, with a 10.973(2), b 10.306(1), c 7.367(3) Å, a 90.03(3), b 109.63(3), g 90.11(2)°, with a crystal-chemical formula Ca 3 (Ca 0.72 Zr 0.28) S1.00 (Zr 0.86 M 0.14) S1.00 (Ca 0.59 Mn 0.25 Fe 0.16) S1.00 (Na 1.20 Ca 0.76) S1.96 (Si 1.98 O 7) 2 (F 2.88 O 1.12) S4.00 , where M represents Nb, Ti, Al, Sr, and REE. Domain I is isostructural with hiortdahlite II, and its crystal structure was refined to a final R of 0.072. Domain II of "guarinite" displays space group P12 1 1, with a 10.836(1), b 10.270(1), c 7.296(1) Å, b 109.13(3)°, with a crystal-chemical formula Ca 3 Zr(Nb 0.56 Fe 0.15 Mn 0.10 Ti 0.10 Zr 0.09) S1.00 (Ca 0.72 Mn 0.18 M 0.10) S1.00 (Na 0.77 Ca 0.23) S1.00 (Na 0.80 Ca 0.22) S1.02 (Si 2 O 7) 2 (O 2.17 F 1.83) S4.00 , where M represents Al, Mg, Sr and Y. Domain II is isostructural with wöhlerite, and its crystal structure was refined to a final R of 0.045. Domain IV of "guarinite" adopts space group P1, with a 10.970(2), b 10.943(2), c 7.365(1) Å, a 109.63(2), b 109.65(2), g 83.39(1)°, with a crystal-chemical formula Ca 4 Zr(Ca 0.31 Mn 0.25 Fe 0.16 Zr 0.14 M 0.14) S1.00 (Na 1.20 Ca 0.76) S1.96 (Si 1.98 O 7) 2 (F 2.88 O 1.12) S4.00 , where M represents Nb, Ti, Al, Sr and REE. Domain IV is isostructural with hiortdahlite I, and its crystal structure was refined to a final R of 0.067. One should note that the refinements of domain I and domain IV (both twinned) have been carried out on the same crystal. EMPA and SEM studies show the presence of chemically homogeneous crystals as well as crystals with distinct chemical zoning due to a wide variation of the major elements Nb, Ca, Na, F, and pointing to the possible coupled substitution Nb 5+ + 2Na + + O 2-→ ← 3Ca 2+ + Fas one of the main mechanisms of chemical variation.
In Materials Science, investigations aiming to prepare new types of molecular sieves (porous mate... more In Materials Science, investigations aiming to prepare new types of molecular sieves (porous materials) that are distinct from zeolites in the kind of polyhedra building up their structure have recently opened a productive field of research inspired by the crystal structures of minerals. Three groups (micro-, mesoand macroporous structures) are discriminated based upon the effective width of the pores (channels). According to the recommendations of the International Union for Pure and Applied Chemistry (IUPAC) (McCusker et al., 2003), pores are micro, meso and macro if the effective width of their channels is less than 2 nm, in the 2-50 nm range and larger than 50 nm, respectively. Ideally, pores repeat in a regular manner, forming long-range ordered structures. Of particular interest are novel molecular sieves characterized by a mixed octahedraltetrahedral framework (heteropolyhedral framework), instead of a purely tetrahedral framework as in zeolites (Figure 1). Heteropolyhedral c...
![Research paper thumbnail of Fiedlerite: Revised Chemical Formula [Pb3Cl4F(OH)·H2O], OD Description and Crystal Structure Refinement of the Two MDO Polytypes](https://attachments.academia-assets.com/99495345/thumbnails/1.jpg)
Mineralogical Magazine, 1994
The chemical formula of fiedlerite, a rare hydrated lead halide, has been revised. The mineral is... more The chemical formula of fiedlerite, a rare hydrated lead halide, has been revised. The mineral is now known to contain also fluorine, and the new, correct formula is Pb3Cl4F(OH)·H2O. X-ray diffraction studies on fiedlerite from Laurion, Greece (the type locality), and from Baratti, Italy (the second known occurrence), revealed its Order-Disorder (OD) character. All structures within this OD family can be built up by layers of the same kind. The two polytypes with Maximum Degree of Order (MDO) display triclinic and monoclinic symmetry, with one and two OD layers, respectively, in the unit cell. On these grounds the nomenclature of fiedlerite has been revised, and the mineral is designated together with the polytype suffix (i.e. fiedlerite-1A, fiedlerite-2M). The crystal structures of the two MDO polytypes of fiedlerite have been solved and refined: fiedlerite-1A: P, a = 8.574(3) Å, b = 8.045(4), c = 7.276(2), α = 89.96(4)° β = 102.05(4), γ = 103.45(4), R = 0.092; fiedlerite-2M: P21/a...
The real structure of tobermorite 11Å: normal and anomalous forms,
European Journal of Mineralogy, 1990
ABSTRACT
![Research paper thumbnail of Order-disorder approach to calcioaravaipaite, [PbCa 2 Al(F,OH) 9 ]: The crystal structure of the triclinic MDO polytype](https://attachments.academia-assets.com/96122171/thumbnails/1.jpg)
American Mineralogist, 2003
The crystal structure of calcioaravaipaite, PbCa 2 Al(F,OH) 9 , was initially solved by direct me... more The crystal structure of calcioaravaipaite, PbCa 2 Al(F,OH) 9 , was initially solved by direct methods in the monoclinic space group A2/m (R = 12.4%). Further study demonstrated the OD nature of the structure, and showed that the crystal was twinned. The structure was solved in the triclinic space group C1-, a = 7.722(3), b = 7.516(3), c = 12.206(4) Å, a = 98.86(1), b = 96.91(1), g = 90.00(1)∞, V = 694.8(3) Å 3 , Z = 4, yielding R = 5.1% for 1420 reflections with F o > 4s(F o). Calcioaravaipaite belongs to a family of order-disorder (OD) structures formed by equivalent layers of symmetry C2/m. Two maximum-degree-of-order (MDO) polytypes are possible. MDO1 results from a regular alternation of stacking operators 2 1/2 and 2-1/2 and yields a monoclinic structure with C2/c, a = 7.72, b = 7.52, c = 24.12 Å, b = 96.99∞. MDO2 results from the sequence 2 1/2 / 2 1/2 / 2 1/2 /… and yields a triclinic structure with a = 7.72, b = 7.52, c = 12.21 Å, a = 98.86, b = 96.91, g = 90.00∞. The structure of calcioaravaipaite is comprised of two kinds of alternating polyhedral slabs parallel to (001). Slab 1 consists of a fluorite-like double layer of edge-sharing (CaF 8) distorted cubes and slab 2 is a composite of face-and edge-sharing (PbF 12) polyhedra and outlying (AlF 6) octahedra, the latter sharing faces and edges with the (PbF 12) polyhedra, but no elements with one another. Aravaipaite and calcioaravaipaite share a common fluorite-type layer; however, in aravaipaite the presence of Pb 2+ rather than Ca 2+ in this layer results in slabs of strikingly different polyhedral configuration.
American Mineralogist, 1999
American Mineralogist, 1996
Laurelite, Pb7F12CI2, from the Grand Reefmine, Graham County, Arizona, is hexagonal, Po, with a =... more Laurelite, Pb7F12CI2, from the Grand Reefmine, Graham County, Arizona, is hexagonal, Po, with a = 10.267(1) and c = 3.9844(4) A and Z = 1. The crystal structure was solved by direct methods and refined to R = 0.035 and RW2= 0.089 for 693 measured reflections (Fo > 9O'Fo)' The structure is related to that of a-PbF2. Both are based upon ninefold-coordinated Pb as tricapped trigonal prisms (TCTPs), which share edges and faces. The two structures can be described with respect to the face-sharing linkages of their TCTPs. The structure of a-PbF2 consists of corrugated sheets of face-sharing TCTPs that interlock by edge-sharing perpendicular to the c axis. In laurelite, the Pb2 TCTPs form three-membered face-sharing clusters about the threefold axis that are propagated into trigonal cylinders by sharing faces in the direction of the c axis. The Pb 1 and Pb3 TCTPs are linked by face-sharing into a three-dimensional framework with corresponding cylindrical voids. Asymmetric coordinations about Pbl and Pb2 are attributed to the stereoactive lone-pair effect. Although the coordinations about the anions appear to disallow substitution of OH for F, stacking defects along the c axis provide a mechanism for accommodating limited OH or H20 for F substitution. A new density determination yielded 7.65(5) glcm3, in reasonable agreement with the density of 7.77 glcm3 calculated on the basis of the empirical formula Pbo.97[F1.6sClo.2s-(H20)o.07]' Z = 7.
American Mineralogist, 2004
Four samples of bakerite, Ca 4 B 5 Si 3 O 15 (OH) 5 , were studied by means of IR, TG/DSC, EPMA, ... more Four samples of bakerite, Ca 4 B 5 Si 3 O 15 (OH) 5 , were studied by means of IR, TG/DSC, EPMA, and X-ray and neutron diffraction. Chemical analyses can readily discriminate bakerite from datolite, Ca 4 B 4 Si 4 O 16 (OH) 4 , by the distinctly lower SiO 2 content of the former. The Rietveld refinement of the combined neutron and X-ray powder data allow the determination of the crystal structure of bakerite to R p 3.09%. The crystal structure can be derived from that of datolite by the substitution 0.25Si 4+ + 0.25O 2-↔ 0.25B 3+ + 0.25(OH)at the Si-centered tetrahedral site. This leads to the crystal chemical formula Ca 4 B 5 Si 3 O 15 (OH) 5. Both of the two hydrogen positions in the bakerite structure, one with full occupancy, the other with 25% occupancy, were precisely located. The water molecule generally thought to be present in bakerite structure is actually absent. The excess water detected in chemical analyses can be attributed to the presence of minor impurities. Given the consistent composition of bakerite from various localities and no evidence for substitution of B for Si in datolite, bakerite is retained as a distinct species. A possible explanation of the peculiar 5:3 boron to silicon ratio in bakerite is provided.
American Mineralogist, 2001
Two new mineral species, carraraite and zaccagnaite, were found in cavities in calcite veins in m... more Two new mineral species, carraraite and zaccagnaite, were found in cavities in calcite veins in marble quarries of the Carrara basin (Apuan Alps, Italy). Carraraite, Ca 3 Ge(OH) 6 (SO 4) 1.08 (CO 3) 0.92 ⋅12H 2 O, occurs as submillimetric crystals, tabular on {001}. The cell dimensions are a = 11.056 (3), c = 10.629 (6) Å, and the space group is P6 3 /m. Carraraite is optically uniaxial (-), ω = 1.509, ε = 1.479. The strongest lines of the X-ray diffraction pattern are at d-spacings (Å): 9.57 (vs) (100), 5.53 (s) (110), 3.83 (s) (112), 3.56 (ms) (202), 2.74 (ms) (302). Carraraite is a new member of the ettringite-thaumasite group, which is characterized by columns of composition [Ca 3 Ge(OH) 6 ⋅12H 2 O] 4+ running along c and interconnected through hydrogen bonding to (SO 4) 2and (CO 3) 2groups. Zaccagnaite, Zn 4 Al 2 (OH) 12 (CO 3)⋅3H 2 O, occurs as minute hexagonal crystals, elongated parallel to [001]. The cell dimensions are a = 3.0725 (3), c = 15.114 (4) Å and the space group is P6 3 /mmc. The crystals are always covered by a thin crust of fraipontite. The strongest lines of the X-ray diffraction pattern are at d-spacings (Å): 7.51 (vs) (002), 3.794 (m) (004), 1.542 (ms) (108), 1.539 (ms) (110). Zaccagnaite is a new member of the hydrotalcite-manasseite family; its structure is characterized by a regular alternation of brucite-like layers with composition (Zn 2/3 Al 1/3)(OH) 2 and an interlayer composed of carbonate groups and water molecules.
Mineralogical Magazine, 2015
The name 'tobermorites' includes a number of calcium silicate hydrate (C-S-H) phases diff... more The name 'tobermorites' includes a number of calcium silicate hydrate (C-S-H) phases differing in their hydration state and sub-cell symmetry. Based on their basal spacing, closely related to the degree of hydration, 14, 11 and 9 Å compounds have been described. In this paper a new nomenclature scheme for these mineral species is reported. The tobermorite supergroup is defined. It is formed by the tobermorite group and the unclassified minerals plombièrite, clinotobermorite and riversideite. Plombièrite ('14 Å tobermorite') is redefined as a crystalline mineral having chemical composition Ca5Si6O16(OH)2·7H2O. Its type locality is Crestmore, Riverside County, California, USA. The tobermorite group consists of species having a basal spacing of ∼11 Å and an orthorhombic sub-cell symmetry. Its general formula is Ca4+x(AlySi6–y)O15+2x–y·5H2O. Its endmember compositions correspond to tobermorite Ca5Si6O17·5H2O (x= 1 andy= 0) and the new species kenotobermorite, Ca4Si6O15(O...
Stibivanite-2O, a new orthorhombic polytype of Sb2VO5, has been found at Buca della Vena mine. It... more Stibivanite-2O, a new orthorhombic polytype of Sb2VO5, has been found at Buca della Vena mine. It occurs as emerald-green acicular and fibrous crystals in a vein of recrystallized dolomite. The space group of the mineral is Pmcn, with a 17.916(3), b 4.790(1), c 5.509(1) angstrom. The strongest lines (visual estimation) in the powder pattern [d in angstrom, intensity in parentheses] are: 3.097(s), 2.986(ms), 9.00 (m), 4.62(m), 1.871(ms), 1.747(mw). The OD character of the structure of monoclinic stibivanite has been established. On the basis of OD theory, a structural model for the orthorhombic modification is proposed. The model has been confirmed through a least-squares refinement, carried out with 530 observed reflections, to a final R of 0.032. The structure of stibivanite-2O, as well as that of the monoclinic polytype, is characterized by the presence of complex ribbons very weakly linked in a and b directions. In the complex ribbons, chains of corner-sharing SbO3 pyramids are a...
Uploads
Papers by Stefano Merlino