Crystallochemical Formula Research Articles

Calcium uranium titanate—A new pyrochlore

Calcium uranium dititanate pyrochlore ( A 2 B 2O 7), a component of a high-level nuclear waste ceramic, was characterized by powder X-ray diffraction, analytical electron microscopy and selected area electron diffraction. The cubic unit cell ( a = 10.1579(5) Å) has symmetry Fd 3m with A in 16( c), B in 16( d), O 1 in 48( f), and O 2 in 8( a). A preliminary examination of the peak intensity in X-ray powder patterns and chemical analyses by energy dispersive X-ray spectroscopy suggest that although this pyrochlore can be approximately described by the crystallochemical formula [Ca, U][Ti 2]O 7 the Ca U ratio may deviate from unity with some trivalent titanium partitioning onto the A-site.

Manganese/iron distribution in a strontian piemontite by neutron diffraction

Crystal structure refinement (R = 0.057 for 811 observed reflections) based on neutron diffraction data of a strontian piemontite (S. Marcel, Italy), with unit cell a = 8.884(3) Å, b = 5.684(1) Å, c = 10.202(3) Å), β = 115.23(2)°, lead to the following crystallochemical formula: Ca(Ca0.84Sr0.16) (Al0.81Mn0.17Fe0.02) Al(Al0.06Mn0.61Fe0.33) [O(SiO4) (Si2O7) OH]. Because of the Jahn-Teller effect, Mn3+ prefers the octahedral site M(3) whose distortion is quite independent from the composition.

Mineral phases and processes within green peloids from two Recent deposits near the Congo River Mouth

AbstractIn the Recent sediments of the Congo River estuary, the green Fe-bearing peloids containing 7 Å phases are nearer to the river mouth than the 10 Å phyllosilicates. Measurements ofd060for 7 Å minerals in various density fractions indicated a progressive transformation of kaolinite into trioctahedral 1:1 phyllosilicates in the zone with a high sedimentation rate. Projection of the chemical composition from the approximate crystallochemical formula on to a classification field confirmed the transformation of kaolinite into a 7 Å Fe-rich phase via substitution of Fe2+and Mg for Al in the octahedral sheet, with insignificant changes in the tetrahedral sheet. The resultant transition phase has a composition closer to greenalite than berthierine. The possible advancement of the evolution process was stopped by massive formation of goethite. The 10 Å minerals formed in the grains deposited in the off-shore sediments have a homogenous composition and occur in association with goethite and quartz. These peloids show an enrichment in Al although no kaolinite is present.

Interpretation of the IR spectra of celadonites and glauconites in the region of OH-stretching frequencies

AbstractA method is given for quantitative analysis of IR spectra of dioctahedral micas in the OH-stretching region, which involves spectral decomposition and correlation of octahedral cation contents with integrated optical densities of the corresponding bands. It provides a basis for the study of order-disorder in these minerals and has allowed revision of the crystallochemical formulae of some glauconites and celadonites.

Crystallochemical classification scheme for molybdates

The authors propose a classification scheme for molybdates of the type R/sub c/A/sub d/ (MoO4)/sub y/ based on analysis of crystallochemical formulas of the structural groups (A/sub d/(MoO3)/sub y/), in the composition of which there are high-valence cations of the complexing agent A and molybdate groups coordinated to them. It has been determined that the 84 studied molybdates are representatives of 32 crystallochemical groups of complexes, in which there are 13 different types of coordination between the tetrahedral MoO4S anions and the A atoms. They have considered the effect of the MoO4:A ratio and the nature of the A cations on the structure and dimensionality of the structural groups. On the basis of the proposed crystallochemical formulas, they have analyzed the interrelationship between the number of bridge oxygen atoms in the AO/sub n/ polyhedra and the method for joining the polyhedra; and they also discuss the reasons for differences in crystal structure between the considered molybdates and sulfates which are analogous in stoichiometric composition.

Textural Variation and Composition of Bentonite Derived from Basaltic Ash

The Rokle bentonite deposit is part of an accumulation of argillized volcanoclastic rocks in the Tertiary stratovolcanic complex of the Doupovske Mountains east of Karlovy Vary (Carlsbad), about 100 km westnorthwest of Prague, Czechoslovakia. The arenite basalt ash was originally composed of hyaloclasts and subordinate biotite. The following types of montmorillonite aggregates were produced during the alteration of the ash in a stagnant, lacustrine environment: (1) extremely fine-grained micro-crystalline aggregates that have honeycomb textures and that replace the original hyaloclasts, and (2) coarse crystalline aggregates that have more open honeycomb textures and that fill pores and cracks in altered hyaloclasts and in pumice vesicles. Both types of aggregates have the same chemical composition according to energy dispersive X-ray analysis. Montmorillonite, separated as the <1-¼m size fraction from olive gray bentonite, has the following crystallochemical formula: (K0.09Na0.02Ca0.29Mg0.10) (Al2.43Fe3+1.05Fe2+0.005Mn2+0.005Mg0.50) (Si7.62Al0.38) O20(OH)4. Biotite was apparently stable during the alteration of the hyaloclasts. Anatase and possible accessory heulandite-clinoptilolite were also formed in small amounts, but were not observed by scanning electron microscopy. Goethite is the youngest oxidation product in some parts of the bentonite. Minute fragments of sodium-rich plagioclase, potassium feldspar, quartz, and muscovite are ubiquitous accessories of the original hyaloclasts. Together with kaolinite, they formed from the underlying fresh or kaolinized orthogneiss.

The structural role of Fe 3+ in biotites from the Euganean Hills, Italy

SummaryPlots of partition coefficient (mineral/matrix) against ionic radius of the elements in seventeen biotites from trachytes and rhyolites of the Euganean Hills do not show differences in the type of diagram between the biotites with tetrahedral sites completely filled by Si and Al, and those in which filling is only possible with the intervention of Fe3+ (or Ti4+) since these sites are incompletely filled by Si and Al. This behaviour seems to exclude, for the latter, the presence of Fe3+ (or Ti4+ in the tetrahedral site. Similar indications are given by structural analysis. The possibility of existence of [(OH)4]4− groups or, more probably, vacancies in these sites is therefore suggested. The consequences that these results would have on the possibility of correct calculation of the crystallo-chemical formula are discussed.

The crystal structure of nagashimalite, Ba4(V3+, Ti)4[(O, OH)2|Cl|Si8B2O27

Nagashimalite, Ba4(V3+3.44Ti0.56)B2Si8O28Cl[(OH)0.44O0.56], a new mineral from the Mogurazawa mine, Gumma Prefecture, is orthorhombic, space group Pmmn, with unit cell parameters a=13.937(3), b=12.122(3), c=7.116(2)A and Z=2.The crystal structure is similar to that of taramellite after Mazzi and Rossi (1965), except for boron and chlorine. It basically consists of a novel borosilicate group [Si8B2O27] which is built up of a pair of Si4O12 groups linked together, sharing corners, by a B2O7 group. These borosilicate groups are in the structure joined together by sharing of octahedra, parallel to b, formed by oxygen atoms about vanadium atoms. The crystallochemical formula is thus given as Ba4(V3+,Ti)4[(O, OH)2|Cl|Si8B2O27]. Mean interatomic distances are: V–O=2. 012(5), Si(1)–O=1.631(4), Si(2)–O=1.617(4), and B–O=1.479(5)A. The Ba atoms are thirteen and eleven-coordinated with mean distances of Ba(1)[13]–(O, OH)=3.094(6), Ba(2)[11]–(O, Cl)=3.121(8), and Ba(3)[11]–(O, Cl)=2.925(8)A.It appears that the reported taramellite structure would in fact contains boron atoms and belongs to the same borosilicate groups as nagashimalite.

X-ray crystallography of krinovite

The unit cell of the meteoritic mineral krinovite, NaMg2CrSia01o, is triclinic with a = 10.22, b = 10.67, c = 8.80 A, IX = 10508', {l =. 960 36', y = 12501'. The monoclinic unit cell given by OLSEN and FUCHS is one of the possible pseudomonoclinic cells. Krinovite is polysynthetically twinned with the b axis of the pseudomonoclinic cell as twin axis. The close relationships among krinovite, aenigmatite and rhonite are shown. The crystal structure of krinovite is suggested and the crystallochemical formula NaVIII2MgVI4CrVI(CrVl)02Sis018 is derived.

X-ray crystallography of krinovite

The unit cell of the meteoritic mineral krinovite, NaMg2CrSia01o, is triclinic with a = 10.22, b = 10.67, c = 8.80 A, IX = 10508', {l =. 960 36', y = 12501'. The monoclinic unit cell given by OLSEN and FUCHS is one of the possible pseudomonoclinic cells. Krinovite is polysynthetically twinned with the b axis of the pseudomonoclinic cell as twin axis. The close relationships among krinovite, aenigmatite and rhonite are shown. The crystal structure of krinovite is suggested and the crystallochemical formula NaVIII2MgVI4CrVI(CrVl)02Sis018 is derived.

Chemical Studies of Minerals Containing Rarer Elements from the Far East District. LXV. Pollucite from Nagatare, Fukuoka Prefecture, Japan

Abstract The chemical analysis of pollucite found in a granite pegmatite at Nagatare, Fukuoka Prefecture, gave SiO2 46.03, Al2O3 17.76, Fe2O3 0.02, MnO 0.01, CaO 0.03, Li2O 0.16, Na2O 2.08, K2O 1.81, Rb2O 0.61, Cs2O 28.88, and H2O 2.74; total 100.13%; recalculated as (Cs,Rb)0.573(Na,K,Li,Mn,Ca)0.316(Al,Fe)0.943Si2.071O6·0.411 H2O as O=6, thus satisfying the crystallochemical formula advocated by Beger. X-ray single crystal and powder studies have shown it to be cubic, the space group is Ia3d; a0=13.674±0.005 Å. It is optically isotropic or very faintly birefringent, with n=1.520±0.002.

Chemical composition and physical properties of lithium-iron micas from the Krušné hory (Erzgebirge), Czechoslovakia and Germany. Part B: Cell parameters and optical data

SummaryUnit-cell dimensions and refractive indices of lithium-iron micas decrease with decreasing iron and increasing lithium. Indices β and γ as well as parameters a and b can be used to estimate the composition of lithium-iron micas but basal spacing and 2Vα are poor indicators of composition.The chemical composition of natural lithium-iron micas from the Krušné hory and the Erzgebirge along the Czechoslovak—German border was discussed in Part A of this study (Rieder et al., 1970). It was concluded that the composition and crystallography of these micas fit best the series siderophyllite-polylithionite. The compositions were expressed by the ratio A′ = LR/(LR+‘Fe’). In this expression, LR is the subscript value of Li or octahedral R3+ (whichever is the smaller) in the crystallochemical formula, ‘Fe’ is the sum of the values in the formula of Fe2+ and Mn2+. A′ therefore defines the position of a particular mica on the siderophyllite-polylithionite join. This paper deals with the correlation between composition, cell dimensions, and refractive indices.

Ammonioborite: New Borate Polyion and Its Structure

The mineral ammonioborite is monoclinic with unit cell dimensions (in angstroms): a = 25.27, b = 9.65, and c = 11.56; beta = 94 degrees 17', and the space group is C 2/c. Analysis of the crystal structure revealed the crystallo-chemical formula (NH(4))(3)B(15)O(20)(OH)(8).4H(2)O, with four such formula units in the unit cell. The basic structural unit is the double ring consisting of one BO(4) tetrahedron and four BO(3) triangles: in ammonioborite three of these units are connected to give trimeric ions [B(15)O(20)(OH)(8)](3-).

Tuhualite Crystal Structure

As judged by crystal structure analysis, the crystallochemical formula of tuhualite is (Na,K)(2)(VI) (Fe(+3))(2)(VI) (Fe(+2))(2)(VI) Si(12)O(30) . H(2)O, with four such formulas in the unit cell. The structure is characterized by six-repeat double chains of silicon tetrahedrons and chains of edge-sharing, alternating iron tetrahedrons and octahedrons. Chains of each kind are connected by corner sharing to four chains of the other type. The iron cations appear to be anomalously ordered with Fe(+2) in tetrahedral and Fe(+3) in octahedral sites.

Kornerupine: Its Crystal Structure

Three-dimensional analysis of the crystal structure of kornerupine reveals the crystallochemical formula Mg(VI)(2)Mg(VI)AlVI(6)[Si(2)O(7)] [(Al,Si)(2) SiO(10)]O(4)(OH), with four formula units in the structure cell of a = 16.100 (2) A, b = 13.767(2) A, c = 6.735(2) A; space group, Cmcm. The unusual crystal structure includes walls of Al-O edge and corner-sharing octahedra, and chains of alternating Mg-O and Al-O octahedra fused to the walls by further edge-sharing to form dense slabs. These slabs are held together by [Si(2)O(7)] corner-sharing tetrahedral pairs and [(Al,Si)(2)SiO(10)] corner-sharing tetrahedral triplets.