: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

2.3. Amorphous Minerals 4354 3. Biological Routes to Controlling Morphology 4354 3.1. General Mechanisms 4356 3.1.1. Soluble and Insoluble Organic Molecules 4356 3.1.2. Control over Crystal Polymorph 4357 3.1.3. Control over Crystal Orientation 4359 3.2. Single-Crystal Biominerals 4359 3.2.1. Organic and Inorganic Soluble Additives 4360 3.2.2. Templating of Single-Crystal Morphologies 4361 3.3. Polycrystalline Biominerals 4366 3.3.1. Nacre Formation in Mollusks 4366 3.3.2. ForaminiferasA Biogenic Mesocrystal 4368 3.4. Amorphous Biominerals 4370 3.4.1. Silicification in Diatoms 4370 3.4.2. In Vitro Studies of Silicification in Diatoms 4371 4. Bioinspired Routes to Controlling Crystal Morphologies 4371

Controlling Mineral Morphologies and Structures in Biological and Synthetic Systems

The precipitation of barium or strontium carbonates in alkaline silica-rich environments leads to crystalline aggregates that have been named silica/carbonate biomorphs because their morphology resembles that of primitive organisms. These aggregates are self-assembled materials of purely inorganic origin, with an amorphous phase of silica intimately intertwined with a carbonate nanocrystalline phase. We propose a mechanism that explains all the morphologies described for biomorphs. Chemically coupled coprecipitation of carbonate and silica leads to fibrillation of the growing front and to laminar structures that experience curling at their growing rim. These curls propagate in a surflike way along the rim of the laminae. We show that all observed morphologies with smoothly varying positive or negative Gaussian curvatures can be explained by the combined growth of counterpropagating curls and growing laminae.

https://science.sciencemag.org/content/sci/323/5912/362.full.pdf

Morphogenesis of self-assembled nanocrystalline materials of barium carbonate and silica.

Cyanobacteria have affected major geochemical cycles (carbon, nitrogen, and oxygen) on Earth for billions of years. In particular, they have played a major role in the formation of calcium carbonates (i.e., calcification), which has been considered to be an extracellular process. We identified a cyanobacterium in modern microbialites in Lake Alchichica (Mexico) that forms intracellular amorphous calcium-magnesium-strontium-barium carbonate inclusions about 270 nanometers in average diameter, revealing an unexplored pathway for calcification. Phylogenetic analyses place this cyanobacterium within the deeply divergent order Gloeobacterales. The chemical composition and structure of the intracellular precipitates suggest some level of cellular control on the biomineralization process. This discovery expands the diversity of organisms capable of forming amorphous calcium carbonates.

https://science.sciencemag.org/content/sci/336/6080/459.full.pdf

An Early-Branching Microbialite Cyanobacterium Forms Intracellular Carbonates

Crystals of a variety of substances including elements, minerals, simple salts, organic molecular crystals, and high polymers forgo long-range translational order by twisting and bending as they grow. These deviations have been observed in crystals ranging in size from nanometers to centimeters. How and why so many materials choose dramatic non-crystallographic distortions is analyzed, with an emphasis on crystal chemistries that give rise to stresses operating either on surfaces of crystallites or within the bulk.

Growth Actuated Bending and Twisting of Single Crystals

The epitaxial role of silica groups in promoting the formation of silica/carbonate biomorphs: A first hypothesis

“Silica Biomorphs” are self-assembled nanocrystals of barium carbonate that form in silica-rich environments. Their morphologies are highly reminiscent of the shapes of primitive life (discovered in Archean cherts), but the precipitates are clearly inorganic and form without intervention of any organic material. The concept of morphology and symmetry has always been used to divide the world into two large groups: the realm of the inanimate and the realm of the living. The object of this study is not to debate the truthfulness of the microfossils, but to understand the laws that control the formation and the shape of polycrystalline structures and to underline the false notion that the living and abiotic realms can be distinguished on the basis of their morphology.

Self-assembled nanocrystals of barium carbonate in biomineral-like structures

Witherite (BaCO3) crystals have been synthesized by mixing BaCl2·2H2O and NaHCO3 aqueous solutions; their growth morphology is characterized by single and twinned individuals both [001] elongated and limited by {110} prism and {hhl} bipyramids. When quartz single crystals are used as substrates, heterogeneous nucleation of witherite occurs onto the {1010}, {1012}, and {0112} forms of quartz and {001} witherite lamellae grow along the [100], [001], and [121] directions of quartz. This witherite/quartz three-dimensional epitaxy is the first evidence that two-dimensional epitaxial layers of quartz can form as well on witherite nucleating from aqueous solutions containing Na-metasilicate. As it is known, nano-polycrystalline structures, the “silica biomorphs”, are precipitated from such solutions: this implies a very high nucleation frequency of witherite. We propose that this is caused by the lowering of the specific surface energy of witherite for the two-dimensional localized adsorption of silica chains.

Witherite (BaCO3)/α-Quartz Epitaxial Nucleation and Growth: Experimental Findings and Theoretical Implications on Biomineralization

The new mineral species grandaite, ideally
 Sr 2 Al(AsO 4 ) 2 (OH), has been discovered on
 the dump of Valletta mine, Maira Valley, Cuneo province, Piedmont, Italy.
 Its origin is related to the reaction between the ore minerals and
 hydrothermal solutions. It occurs in thin masses of bright orange to salmon
 to brown coloured crystals, or infrequently as fan-like aggregates of small
 (<1 mm) crystals, with reddish-brown streak and waxy to vitreous lustre.
 Grandaite is associated with aegirine, baryte, braunite, hematite, tilasite,
 quartz, unidentified Mn oxides and Mn silicates under study. Grandaite is biaxial (+) with refractive indices α = 1.726(1), β = 1.731(1),
 γ = 1.752(1). Its calculated density is 4.378 g/cm 3 . Grandaite is
 monoclinic, space group P 2 1 / m ,
 with a = 7.5764(5), b = 5.9507(4),
 c = 8.8050(6) A, β = 112.551(2)°, V =
 366.62(4) A 3 and Z = 2. The eight strongest
 diffraction lines of the observed X-ray powder diffraction pattern are
 [ d in A, ( I ), ( hkl )]:
 3.194 (100)( 11), 2.981
 (50.9)(020), 2.922 (40.2)( 03), 2.743
 (31.4)(120), 2.705 (65.2)(112), 2.087 (51.8) ( 23), 1.685 (24.5)(321), 1.663 (27.7)(132). Chemical
 analyses by electron microprobe gave (wt.%) SrO 29.81, CaO 7.28, BaO 1.56,
 Al 2 O 3 7.07, Fe 2 O 3 2.34,
 Mn 2 O 3 1.88, MgO 1.04, PbO 0.43,
 As 2 O 5 44.95, V 2 O 5 0.50,
 P 2 O 5 0.09, sum 96.95; H 2 O 1.83 wt.% was
 calculated by stoichiometry from the results of the crystal-structure
 analysis. Raman and infrared spectroscopies confirmed the presence of
 (AsO 4 ) 3− and OH groups. The empirical formula
 calculated on the basis of 9 O a.p.f.u., in agreement with the structural
 results, is
 (Sr 1.41 Ca 0.64 Ba 0.05 Pb 0.01 ) ∑=2.11 (Al 0.68 Fe 0.14 3+ Mn 0.12 3+ Mg 0.13 ) ∑=1.07 [(As 0.96 V 0.01 ) ∑=0.97 O 4 ] 2 (OH),
 the simplified formula is
 (Sr,Ca) 2 (Al,Fe 3+ )(AsO 4 ) 2 (OH)
 and the ideal formula is
 Sr 2 Al(AsO 4 ) 2 (OH). The crystal structure was solved by direct methods and found to be
 topologically identical to that of arsenbrackebuschite. The structure model
 was refined on the basis of 1442 observed reflections to R 1 = 2.78%. In the structure of grandaite, chains of edge-sharing
 M 3+ octahedra run along [010] and share vertices with
 T 5+ tetrahedra, building up [ M 3+ ( T 5+ O 4 ) 2 (OH, H 2 O)] units, which
 are connected through interstitial divalent cations. Grandaite is named
 after the informal appellation of the province where the type locality is
 located. The new mineral was approved by the International Mineralogical
 Association Commission on New Minerals, Nomenclature and Classification
 (IMA2013-059). The discovery of grandaite and of other members of the group
 (description still in progress) opens up the possibility of exploring the
 crystal chemistry of the brackebuschite supergroup.

Arsenic-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: I. Grandaite, Sr2Al(AsO4)2(OH), description and crystal structure

The new mineral species braccoite, ideally Na![Formula][1] [Si5AsO17(OH)](OH), has been discovered in the Valletta mine dumps, in Maira Valley, Cuneo province, Piedmont, Italy. Its origin is probably related to the reaction between ore minerals and hydrothermal fluids. It occurs as subhedral crystals in brown-red coloured thin masses, with a pale-yellow streak and vitreous to resinous lustre. Braccoite is associated with tiragalloite, for which new data are provided, as well as gamagarite, hematite, manganberzeliite, palenzonaite, quartz, saneroite, tokyoite, unidentified Mn oxides, organic compounds, and Mn arsenates and silicates under study.

Braccoite is biaxial positive with refractive indices α = 1.749(1), β = 1.750(1), γ = 1.760(1). It is triclinic, space group P 1I, with a = 9.7354(4), b = 9.9572(3), c = 9.0657(3) A, α = 92.691(2), β = 117.057(4), γ = 105.323(3)°, V = 740.37(4) A3 and Z = 2. Its calculated density is 3.56 g/cm3. The ten strongest diffraction lines of the observed powder X-ray diffraction (XRD) pattern are [ d in A, ( I ), ( hkl )]: 3.055 (69)(22I1), 3.042 (43)(102), 3.012 (65)(32I1I), 2.985 (55)(23I1I), 2.825 (100)(213I), 2.708 (92)(220), 2.627 (43)(23I2I), 2.381 (58)(41I1I), 2.226 (25)(214I) and 1.680 (433I)(36). Chemical analyses by wavelength-dispersive spectroscopy electron microprobe gave (wt.%): Na2O 4.06, CaO 0.05, MnO 41.76, MgO 0.96, Al2O3 0.04, CuO 0.02, SiO2 39.73, As2O5 6.87, V2O5 1.43, SO3 0.01 and F 0.04. H2O 2.20 was calculated on the basis of 2OH groups p.f.u. Raman spectroscopy confirmed the presence of (SiO4)4−, (AsO4)3− and OH groups. The empirical formula, calculated on the basis of Σ cations-(Na,K) = 11 p.f.u., in agreement with the results of the crystal structure, is Na1.06(![Formula][2] ![Formula][3] Mg0.19![Formula][4] Al0.01Ca0.01)[Si5(As0.48Si0.37![Formula][5] )O17(OH)](OH0.98F0.02); the simplified formula is Na(Mn,Mg,Al,Ca)5[Si5(As,V,Si)O17(OH)](OH,F).

Single-crystal XRD allowed the structure to be solved by direct methods and revealed that braccoite is the As-dominant analogue of saneroite. The structure model was refined on the basis of 4389 observed reflections to R 1 = 3.47%. Braccoite is named in honour of Dr Roberto Bracco (b. 1959), a systematic minerals collector with a special interest in manganese minerals. The new mineral was approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA 2013-093).

 [1]: /embed/mml-math-2.gif
 [2]: /embed/mml-math-3.gif
 [3]: /embed/mml-math-4.gif
 [4]: /embed/mml-math-5.gif
 [5]: /embed/mml-math-6.gif

/pdf/as-bearing-new-mineral-species-from-valletta-mine-maira-34c444kyy7.pdf

As-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: II. Braccoite, NaMn2+5[Si5AsO17(OH)](OH), description and crystal structure

Erica Bittarello

Papers

The epitaxial role of silica groups in promoting the formation of silica/carbonate biomorphs: A first hypothesis

Self-assembled nanocrystals of barium carbonate in biomineral-like structures

Witherite (BaCO3)/α-Quartz Epitaxial Nucleation and Growth: Experimental Findings and Theoretical Implications on Biomineralization

Arsenic-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: I. Grandaite, Sr2Al(AsO4)2(OH), description and crystal structure

As-bearing new mineral species from Valletta mine, Maira Valley, Piedmont, Italy: II. Braccoite, NaMn2+5[Si5AsO17(OH)](OH), description and crystal structure