Showing papers in "Canadian Mineralogist in 1969"

Structural stability of minerals with the pyrite, marcasite, arsenopyrite and lollingite structures

Abstract: Structural stabilities of disulfides, diarsenides and sulfarsenides of iron, cobalt and nickel are explained on the basis of ligand field theory, and can be correlated with the number of nonbonding d electrons of the metal atom in the structure, and explained by the tendency of compounds to form structures in which maximum electron spin-pairing takes place. Minerals with pyrite structure are characterized by metal-sulfur octahedra joined at corners, with no apparent interaction between d electrons of neighboring metal atoms. Other structures are characterized by shared octahedral edges along one direction, so that metal atoms are brought into close proximity. In minerals with marcasite structure, there is sharing of octahedral edges, but subtending angles are less than 90 degrees , indicating metal-metal repulsion. In lollingite the large subtending angle and short intermetallic distance signify interaction between adjoining metal atoms.

On the origin of reverse pleochroism' of a phlogopite

Abstract: The visible spectra of phlogopite with a reversely pleochroic scheme consist essentially of three bands in the 450-550 mmu region superimposed on the wing of a strongly pleochroic band centered in the ultraviolet region. The spectra have their greatest intensity when polarized light vibrates normal to the cleavage plane, the reverse of micas with normal pleochroic schemes. By comparing the phlogopite spectra with those of an iron orthoclase and FeCl 4 (super -) , materials which are known to contain tetrahedrally-coordinated Fe (super 3+) , it has been established that the three-band system in the visible region is also due to this ion. The background absorption is considered to be due to an O (super 2-) Fe (super 3+) charge-transfer band which is most intense when the vibration direction is coincident with the O (super 2-) (unbridged)--Fe bond perpendicular to (001) in the iron-bearing tetrahedra.

On the origin of colour and pleochroism of kyanite

Abstract: Although the colour and pleochroism of blue kyanite has been attributed to the presence of Ti (super 3+) by previous workers, the present study of the polarized absorption spectra of such kyanite indicates that Fe (super 2+) Fe (super 3+) charge transfer accounts more readily for the optical properties. Experimental evidence is given for the presence of both Fe (super 2+) and Fe (super 3+) in blue kyanite and proposals are made for the manner in which these ions interact, across octahedral edges, to give rise to a pleochroic absorption band at 16500-1700 cm (super -1) . The direction of maximum intensity of this band correlates directly with the principal optical direction, Z, of kyanite.

The optical absorption spectrum of tetrahedrally bonded Fe (super 3+) in orthoclase

Abstract: Optical absorption spectrum measurements and spectral details are presented together with transition assignments and other interpretations for a lemon-yellow gem-quality specimen of iron-rich orthoclase. Only three principal bands--26500, 24000, and 22600 cm (super -1) --are resolved in the spectrum and are tentatively assigned to the 6 A 14 A 14 E(G), 6 A 14 T 2 (G) and 6 A 14 T 1 (G) transitions, respectively. The resolution of these bands only is due to encroachment into the visible region of intense background absorption centered in the ultraviolet probably due to the O (super 2-) Fe (super 3+) charge-transfer process. The sharpness of the 26500 cm (super -1) band is consistent with assignment to transition of the first field-independent state. The yellow color is due to absorption of blue light in the 400 to 450 m mu region.

An optical absorption study of the origin of colour and pleochroism in pink and brown tourmalines

Abstract: Simple ligand-field theory is used in assigning absorption bands of polarized tourmaline spectra to specific transition-metal ions in specific environments. The pleochroic properties of the bands are correlated with some structural properties of the crystal. It is suggested that the colour of pink and brown tourmalines is due to d-d electronic transitions in octahedrally-bonded Mn (super 3+) and Ti ions, respectively. Pink tourmalines have an absorption band at 19,000 cm (super -1) (520 mmu ) and brown tourmalines at 22,000 cm (super -1) (450 mmu ). The bands in both systems have maximum intensity when the electric vector of incident light is vibrating in the 001 plane; the probable causes of the pleochroism are discussed. It is also concluded that the transition metal ions are located mainly in the trigonal brucite units.

Zoned and unzoned garnets from the Grenville gneisses around Gananoque, Ontario

Abstract: Strict limitations are placed on reacting chemical systems during metamorphism if one or more of the mineral phases is compositionally zoned. An investigation of the volumes of equilibrium in some high-grade metamorphic rocks from the Grenville of southeastern Ontario, therefore, included a study of possible zoning of the garnets. Traverses at 25 micron steps across four garnets, employing a laser-excited spectrochemical technique, revealed no compositional zoning with respect to Fe, Mg, Mn or Ca in three of the grains. High Mn values, however, occur in the central portion of one garnet within an area of quartz inclusions. It is proposed that the garnets of these rocks were originally zoned and that later metamorphic events have eliminated this zoning in most of the garnets, some still showing a relic zoning in their central portions.

Optical absorption spectra of chormium-bearing tourmaline, black tourmaline and buergerite

Abstract: Polarized absorption spectra are reported of Cr-bearing tourmaline from Kaavi, Finland, two black tourmalines from Villeneuve, Quebec, and Como, Italy, and buergerite from San Luis Potosi, Mexico. Spectra of Cr-bearing tourmaline exhibit two strong absorption bands at 17000 cm (super -1) , characteristic of Cr (super 3+) , energy of the former band indicating that Cr (super 3+) is located in a "loose site' in the octahedral sites in the spiral chain. Spectra of black tourmalines consist of bands marking transitions within Fe (super 2+) and Fe (super 3+) ions; Mn (super 3+) may also be present in black tourmalines. Buergerite spectra show bands due to Fe (super 2+) in near infrared and red regions, but most features in the visible are swamped by charge-transfer bands. Fe is located in Al (super 3+) sites in spiral chains of black tourmalines, but mainly in "brucite units' of buergerite.

On the origin of colour and pleochroism in andalusite from Brazil

Abstract: A study is reported of the polarized optical absorption spectra of a specimen of andalusite from Brazil. The weakly visible pleochroism of relatively thick a-b sections is thought to be the result of variation in the intensity of a u.v.-centered band due to O (super 2-) Fe (super 3+) charge transfer. Arguments are presented to show why absorption is more intense in the E b spectrum. Intense pleochroism of andalusite sections containing the c-axis is considered to be the result of Ti (super 3+) Ti (super 4+) charge transfer via overlapping t 2g orbital lobes of adjacent lobes of adjacent ions located in the chains of octahedra that parallel the c-axis. Absorption is at a maximum when polarized light vibrates along the c-axis, the direction in which t 2g orbital lap occurs.

Quantitative determination of hexagonal and monoclinic pyrrhotites by X-ray diffraction

Abstract: Measurement of difference in amplitude of components at about 51.75 degrees and 51.40 degrees 2theta (Co Kalpha radiation) of the asymmetric X-ray diffraction peak resulting from partial superposition of strong diffractions from corresponding planes in hexagonal and monoclinic pyrrhotite structures allows rapid quantitative determination of amounts and proportions of these structures in certain sulfide ores carrying at least 3 percent of either pyrrhotite type. The differences in amplitudes from synthetic mixtures of the pure structures are divided by amplitudes of a nearby diffraction peak from an internal standard added in constant proportion; resulting ratios are plotted against known proportions of either structure. The plot may be checked against weights of magnetic concentrates of monoclinic pyrrhotites from ores under study.

Two-phase hexagonal pyrrhotites

Abstract: Microscopic and X-ray diffraction studies on two natural specimens of two-phase hexagonal pyrrhotites show that the two unmixed phases have a common crystallographic orientation. In polished section, the common c-axis is in the same plane as the short diagonals of the rhombic sections formed by the intersection of the exsolution lamellae. The superstructures of the intermediate hexagonal pyrrhotite in the two samples are different from one another and have not been reported previously from natural material, being hexagonal 2A,6C and hexagonal 2A,4C, where A and C refer to the a and c parameters of the subcell.

A spectral study of the origin of colour and pleochroism of a of a titanaugite from Kaiserstuhl and of a riebeckite from Saint Peter's Dome, Colorado

Abstract: Polarized spectra of a-b sections of titanaugite (from Germany) show a pleochroic band at about 14000 cm (super -1) assigned to Fe (super 2+) Fe (super 3+) charge-transfer. Intra-cationic d-d bands of octahedrally-bonded Fe (super 2+) , Fe (super 3+) , and Ti (super 3+) were observed at 10000 cm (super -1) , 22000 cm (super -1) , and 19000 cm (super -1) respectively. Polarized spectra of a-c sections of riebeckite from St. Peter's Dome, Colorado, show pleochroic band at 15700 cm (super -1) polarized along metal-metal directions; it is assigned to Fe (super 2+) Fe (super 3+) charge-transfer. The field-independent transition 6 A 14 A 14 E(G) in Fe (super 3+) is observed at 23000 cm (super -1) . Intra-cation d-d bands of Fe (super 2+) appear as weak shoulders on the limb of the 15700 cm (super -1) band.

Optical absorption studies of grossularite, andradite (var. colophonite) and uvarovite

Abstract: The spectra of one colophonite, two grossularites, and one uvarovite are reported. Identification of the band marking electronic transitions to the second field-independent state in octahedrally-bonded Fe 3 was the purpose of the study.

Dresserite, the new barium analogue of dundasite

Abstract: Dresserite occurs with weloganite in cavities in an alkalic sill intruding limestone at St-Michel, Montreal Island, Quebec. Chemical analysis corresponds to Ba (sub 1.98) Al (sub 4.06) C (sub 4.06) O 23 H (sub 13.67) , ideally Ba 2 Al 4 (CO 3 ) 4 (OH) 8 X3H 2 O. This is the barium analog of the lead mineral, dundasite. Dresserite occurs as white spherical aggregates averaging about 2 mm in diameter, each of tapering fibers elongated parallel to c. It is biaxial negative with 2V = 30 degrees to 40 degrees ; extinction is parallel. The mineral is orthohombic a = 9.27, b = 16.83; c = 5.63 A; the space group can be Pbmm, Pb2 1 m, or Pbm2. The X-ray powder pattern superficially resembles that of dundasite. Strongest pattern lines and a complete listing of observed spectra are given with those of dundasite for comparison.

The nature of the synthetic crystalline basic aluminum sulphates as compared with basaluminite

Abstract: Basaluminite, Al 4 (OH) 10 SO 4 X5H 2 O from Northamptonshire and Kansas showed reversible expansion and contraction equivalent to 1 layer of interlayer adsorbed water between 100 percent and 0 percent (over P 2 O 5 ) relative humidity. This characteristic supports the previous suggestion that the crystalline basic aluminum sulfate formed upon aging the partially neutralized solution of Al 2 (SO 4 ) 3 in the presence of montmorillonite was basaluminite. In the absence of clay, the crystalline basic aluminum sulfates that formed at 50 degrees C, had compositions, thermal analysis features, and solubility products similar to basaluminite but had a slightly different crystalline form.

The birefringence and dichroism of silicon carbide polytypes

Abstract: The birefringence of 11 synthetic nitrogen-doped silicon carbide polytypes has been measured using an interference fringe method in prisms cut from syntactically intergrown polytypic crystals. Data are tabulated.

New observations on matildite

Abstract: A study of matildite from another occurrence in the Camsell River area, N.W.T. is reported. The mineral occurs as pure irregular grains in a deposit containing native silver, native bismuth and Co-Ni arsenides and in which galena has not been identified. Single crystal studies and reflectivity measurements confirm the hexagonal symmetry postulated by Geller and Wernick, but with the a-cell dimension doubled, yielding values of a = 8.12; c = 19.02A. Electron-probe microanalysis shows that the mineral is homogeneous with a formula of Ag (sub 0.95) Bi (sub 1.00) S (sub 1.97) which agrees very well with the ideal formula AgBiS 2 . Microhardness values (25-gram load) range from VHN 59 to 76.

Neyite; a new sulphosalt from Alice Arm, British Columbia

Abstract: Neyite, Pb 7 Bi 6 (Cu,Ag) 2 S 17 , is a new sulfosalt mineral occurring as needles and acicular aggregates in late vuggy quartz veins with pyrite, galena, sphalerite, chalcopyrite, aikinite, cosalite, and tetrahedrite. These veins are later than the quartz-molybdenite veins of Lime Creek molybdenum deposit near Alice Arm, B.C. The mineral is lead grey with bright metallic luster and Prussian blue tarnish on exposure; it is brittle with conchoidal fracture, and has a hardness of 2.5 with specific gravity of 7.02. It has monoclinic symmetry and a = 37.5 + or - 0.1, b = 4.07 + or - 0.01, c = 41.6 + or - 0.1 A, and beta = 96.8 degrees + or - 0.3 degrees . Strongest lines of the X-ray powder diffraction pattern and reactions to standard etch tests are given.

On the origin of colour and pleochroism of astrophyllite and brown clintonite

Abstract: In a spectral study, sections of both minerals cut parallel and perpendicular to the 001 (cleavage) plane were examined in polarized light. Both show a non-pleochroic two-band system in the near-infrared region that is assigned to d-d transitions in octahedrally-bonded Fe (super 2+) , and exhibit a strong pleochroic absorption band in the blue end of the spectrum that is the obvious cause of color and pleochroism of the minerals. The band is observed as 23,000 cm (super -1) in astrophyllite, and has maximum intensity when E coincides with the orientation of Ti-O-Ti units. The band is observed at 22,000 cm (super -1) in clintonite with maximum intensity when E coincides with the plane of d-orbital overlap between neighbouring cations in the octahedral layer. (E represents the vibration direction of the electric vector of incident light). In both minerals, the band is assigned to Ti (super 3+) -Ti (super 4+) electronic interaction.

Epididymite from Mont Saint Hilaire, Quebec

Abstract: Two types of epididymites have been found at Mont St. Hilaire. The first consists of euhedral crystals which are tapering pseudo-hexagonal prisms, most only a few millimeters long; all have a soft grayish-brown covering. The second type consists of radiating groups of translucent to transparent lath-shaped crystals, elongated parallel to the b-axis. X-ray powder diffraction data are tabulated.

A note on the unit cell constants, and X-ray diffraction powder pattern, of pyrobelonite

Abstract: The unit cell dimensions of pyrobelonite have been remeasured using a Picker automatic diffractometer and Cu radiation. New data are: orthorhombic, Pnam, a = 7.644, b = 9.508, c = 6.182 Z; U = 449.3025 A 3 , F. W. = 1576.30; D x = 5.824 g ml (super -1) ; A = 4; D m = 5.82 g ml (super -1) . Dimensions previously reported are compared with remeasured values in a table. Indexed X-ray diffraction powder data with d values calculated on a computer are listed in a table.

Secondary violarite and bravoite, English Lake, Manitoba

Abstract: Supergene or hypogene alteration of a pentlandite-chalcopyrite-pyrite assemblage has resulted in the formation of a number of secondary sulfides. Violarite formed first and occurs pseudomorphically after pentlandite. Alteration later intensified, resulting in the dissolution of violarite, chalcopyrite and pyrite and the concomitant deposition of bravoite, idiomorphic pyrite, anhedral pyrite, marcasite, chalcopyrite, hematite, quartz and carbonate. Bravoite, in contrast to violarite, does not occur pseudomorphically after pentlandite. This relationship is considered to be of general application. The nickel content of each sulfide was determined using an electron microprobe analyzer. Relationships between idiomorphic pyrite and bravoite show that an immiscibility gap may exist between pyrite, with up to 1.5 percent Ni, and bravoite, with 11 to 12 percent Ni.

Fabianite and its synthetic dimorph, CaB 3 O 5 (OH); new data

Abstract: The structure and other crystallographic properties of the synthetic compound CaB 3 O 5 (OH) were reported by Clark et al (1962) and a crystallographic description of the new mineral fabianite, of the same composition, was published by Kuhn et al (1962). In this study the space group and unit-cell parameters of fabianite were determined, and the optical properties and crystal habits of both dimorphs were redetermined. Results are tabulated with those of the previous investigators for comparison.

Ramsdellite and groutite from Nova Scotia

Abstract: The ramsdellite comes from Cape Split, Kings County, and the groutite from the Walton mine, Hants County. The latter is the first reported from Nova Scotia. The complex paragenesis of minerals in the Walton area is reviewed, and X-ray diffraction data, comparison of unit cell dimensions, and trace-element determinations are tabulated.