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E.E. Foord

Publications and source records attributed to E.E. Foord.

At least 19 recordsLinked to original sources
USGS2018

A reexamination of the turquoise group: The mineral aheylite, planerite (redefined), turquoise and coeruleolactite

The turquoise group has the general formula: A (sub 0-1) B 6 (PO 4 ) (sub 4-x) (PO 3 OH) x (OH) 8 .4H 2 O, where x = 0-2, and consists of six members: planerite, turquoise, faustite, aheylite, chalcosiderite and an unnamed Fe (super 2+) -Fe (super 3+) analogue. The existence of "coeruleolactite" is doubtful. Planerite is revalidated as a species and is characterized by a dominant A-site vacancy. Aheylite is established as a new member of the group, and is characterized by having Fe (super 2+) dominant in the A-site. Chemical analyses of 15 pure samples of microcrystalline planerite, turquoise, and aheylite show that a maximum of two of the (PO 4 ) groups are protonated (PO 3 OH) in planerite. Complete solid solution exists between planerite and turquoise. Other members of the group show variable A-site vacancy as well. Most samples of "turquoise" are cation-deficient or are planerite. Direct determination of water indicates that there are 4 molecules of water. Planerite, ideally []Al 6 (PO 4 ) 2 (PO 3 OH) 2 (OH) 8 .4H 2 O, is white, pale blue or pale green, and occurs as mamillary, botryoidal crusts as much as several mm thick; may also be massive; microcrystalline, crystals typically 2-4 micrometres, luster chalky to earthy, H. 5, somewhat brittle, no cleavage observed, splintery fracture, D m 2.68(2), D c 2.71, not magnetic, not fluorescent, mean RI about 1.60. a 7.505(2), b 9.723(3), c 7.814(2) Aa, alpha 111.43 degrees , beta 115.56 degrees , Gamma 68.69 degrees , V 464.2(1) Aa 3 , Z = 1. Aheylite, ideally Fe (super 2+) Al 6 (PO 4 ) 4 (OH) 8 .4H 2 O, is pale blue or green, and occurs as isolated and aggregate clumps of hemispherical or spherical, radiating to interlocked masses of crystals that average 3 micrometres in maximum dimension; porcelaneous-subvitreous luster, moderate to brittle tenacity, no cleavage observed, hackly to splintery fracture, not magnetic, not fluorescent, biax. (+), mean RI is about 1.63, D m 2.84(2), D c 2.90. a 7.400(1), b 9.896(1), c 7.627(1) Aa, alpha 110.87 degrees , beta 115.00 degrees , gamma 69.96 degrees , V 460.62(9) Aa 3 , Z = 1.

Mineralogical Magazine↗
USGS2018

Proposed nomenclature for samarskite-group minerals: new data on ishikawaite and calciosamarskite

The current definition of samarskite-group minerals suggests that ishikawaite is a uranium rich variety of samarskite whereas calciosamarskite is a calcium rich variety of samarskite. Because these minerals are chemically complex, usually completely metamict, and pervasively altered, their crystal chemistry and structure are poorly understood. Warner and Ewing (1993) proposed that samarskite is an A 3+ B 5+ O 4 mineral with an atomic arrangement related to α-PbO 2 . X-ray diffraction analyses of the recrystallized type specimen of ishikawaite and the Ca-rich samarskite reveal that they have the same structure as samarskite-(Y) recrystallized at high temperatures. Electron microprobe analyses show that the only significant difference between samarskite-(Y), ishikawaite, and calciosamarskite lies in the occupancy of the A -site. The A -site of samarskite-(Y) is dominated by Y+ REE whereas the A -site of ishikawaite is dominantly U+Th and calciosamarskite is dominantly Ca. Additionally, a comparison of these data to those of Warner and Ewing (1993) show that in several cases Fe 2+ or Fe 3+ are dominant in the A -site. We propose that the name samarskite-( REE +Y) should be used when one of these elements is dominant and that the mineral be named with the most abundant of these elements as a suffix. The name ishikawaite should be used only when U+Th are dominant and the name calciosamarskite should only be used when Ca is the dominant cation at the A -site. Finally, because of the inability to quantify the valence state of iron in these minerals, the exact nature of the valence state of iron in these minerals could not be determined in this study.

Mineralogical Magazine↗
USGS2005

Terlinguacreekite, Hg2+3O2 Cl2, a new mineral species from the Perry pit, Mariposa mine, Terlingua mining district, Brewster County, Texas, U.S.A

Terlinguacreekite, ideally Hg 2+ 3 O 2 Cl 2 , has a very pronounced subcell that is orthorhombic, space-group choices Imam , Imcm , Ima 2 and I 2 cm , with unit-cell parameters refined from powder data: a 6.737(3), b 25.528(10), c 5.533(2) Å, V 951.6(6) Å 3 , a:b:c 0.2639:1:0.2167, Z = 8. The true symmetry, supercell unit-cell parameters, and details regarding the crystal structure are unknown. The strongest nine lines of the X-ray powder-diffraction pattern [ d in Å ( I )(subcell hkl )] are: 5.413(30)(011), 4.063(80)(121), 3.201(50)(080), 3.023(50)(161), 2.983(60)(240), 2.858(30)(211), 2.765(50)(002), 2.518(100b)(091, 251) and 2.026(30)(242). The mineral is found in an isolated area measuring approximately 1 × 0.5 m in the lower level of the Perry pit, Mariposa mine, Terlingua mining district, Brewster County, Texas (type locality), as mm-sized anhedral dark orange to reddish orange crusts of variable thickness on calcite, and rarely as 0.5 mm-sized aggregates of crystals of the same color. It has also been identified at the McDermitt mine, Humboldt County, Nevada, U.S.A., where it occurs with kleinite and calomel in silicified volcanic rocks and sediments. Terlinguacreekite is a secondary phase, most probably formed from the alteration of primary cinnabar or native mercury. At Terlingua, most crusts are thin, almost cryptocrystalline, with no discernable forms, and are resinous and translucent to opaque. Crystals are up to 0.2 mm in length, subhedral, acicular to prismatic, elongation [001], with a maximum length-to-width ratio of 4:1. They are vitreous, transparent, and some crystals have brightly reflecting faces, which may be {010} and {110}. The streak is yellow, and the mineral is brittle with an uneven fracture, no observable cleavage, and is soft, nonfluorescent under both long- and short-wave ultraviolet light. D (calc.) is 9.899 g/cm 3 (empirical formula). Material from the McDermitt mine is reversibly photosensitive, and turns from vivid orange to black in strong light. In reflected plane-polarized light, it is bluish grey, with very weak (in air) to distinct (in oil) bireflectance, nonpleochroic, and distinctly anisotropic, with colors masked by ubiquitous yellowish orange to orange internal reflections. Measured values of reflectance obtained in air and in oil are tabulated. Averaged results of electron-microprobe analysis give HgO 92.03, Cl 9.54, Br 1.22, sum 102.79, less O = Cl + Br 2.28, total 100.51 wt.%. The empirical formula is Hg 2+ 3.00 O 2.00 (Cl 1.90 Br 0.11 ) ∑2.01 , based on O + Cl + Br = 4 atoms per formula unit. The mineral name recalls the creek that flows through the Terlingua mining district and into the Rio Grande River.

Texas↗
USGS2004

Nevadaite, (Cu2+, Al, V3+)6 [Al8 (PO4)8 F8] (OH 2 (H2O)22, a new phosphate mineral species from the Gold Quarry mine, Carlin, Eureka County, Nevada: Description and crystal structure

Nevadaite, (Cu 2+ , □, Al, V 3+ ) 6 (PO 4 ) 8 F 8 (OH) 2 (H 2 O) 22 , is a new supergene mineral species from the Gold Quarry mine, near Carlin, Eureka County, Nevada, U.S.A. Nevadaite forms radiating clusters to 1 mm of prismatic crystals, locally covering surfaces more that 2 cm across; individual crystals are elongate on [001] with a length:width ratio of > 10:1 and a maximum diameter of ~30 μm . It also occurs as spherules and druses associated with colorless to purple-black fluellite, colorless wavellite, strengitevariscite, acicular maroon-to-red hewettite, and rare anatase, kazakhstanite, tinticite, leucophosphite, torbernite and tyuyamunite. Nevadaite is pale green to turquoise blue with a pale powder-blue streak and a vitreous luster; it does not fluoresce under ultra-violet light. It has no cleavage, a Mohs hardness of ~3, is brittle with a conchoidal fracture, and has measured and calculated densities of 2.54 and 2.55 g/cm 3 , respectively. Nevadaite is biaxial negative, with 1.540, β 1.548, γ 1.553, 2 V (obs.) = 76°, 2 V (calc.) = 76° , pleochroic with X pale greenish blue, Y very pale greenish blue, Z blue, and with absorption Z ≫ X > Y and orientation X = c, Y = a, Z = b. Nevadaite is orthorhombic, space group P 2 1 mn , a 12.123(2), b 18.999(2), c 4.961(1) Å, V 1142.8(2) Å 3 , Z = 1, a:b:c = 0.6391:1:0.2611 . The strongest seven lines in the X-ray powder-diffraction pattern [ d in Å(I)( hkl )] are: 6.077(10)(200), 5.618(9)(130), 9.535(8)(020), 2.983(6)(241), 3.430(4)(041), 2.661(4)(061), and 1.844(4)(352). A chemical analysis with an electron microprobe gave P 2 O 5 32.54, Al 2 O 3 27.07, V 2 O 3 4.24, Fe 2 O 3 0.07, CuO 9.24, ZnO 0.11, F 9.22, H 2 O (calc.) 23.48, OH ≡ F–3.88, sum 102.09 wt.% ; the valence states of V and Fe, and the amount of H 2 O , were determined by crystal-structure analysis. The resulting empirical formula on the basis of 63.65 anions ( including 21.65 H 2 O pfu ) is ( (Cu 2.00 2+ Zn 0.02 V 0.98 3+ Fe 0.01 3+ Al 1.15 ) ∑ 4.16 Al 8 P 7.90 O 32 [F 8.37 (OH) 1.63 ] ∑10 (H 2 O) 21.65 . The crystal structure of nevadaite was solved by direct methods and refined to an R index of 4.0% based on 1307 observed reflections collected on a four-circle diffractometer with Mo K α X-radiation . The structure consists of ordered layers of vertex-sharing octahedra and tetrahedra alternating with layers of disordered vertex-sharing and face-sharing octahedra in the b direction. [Alϕ 5 ] chains of octahedra are decorated by (PO 4 ) tetrahedra that share vertices with octahedra adjacent in the chain . These chains link in the c direction by sharing vertices between octahedra and tetrahedra to form an ordered layer of the form [Al 8 (PO 4 ) 8 F 8 (H 2 O) 8 ] . In the disordered layer, octahedra containing positionally disordered Cu 2+ , V 3+ , Al and □ (vacancy) share trans faces to form columns that link by sharing octahedron vertices to form ribbons extending in the c direction; the resulting layer has the form {(Cu 2 2+ □ 2 V 3+ ,Al) ∑6 (H 2 O) 12 (OH) 2 (H 2 O) x }, x ≈ 2 . The layers link in the b direction by sharing vertices between octahedra and tetrahedra. Although decorated chains topologically equivalent to that in nevadaite are common in many oxysalt minerals, its chain is geometrically distinct from those topologically equivalent chains. The M – M linkage along the [ M ϕ 5 ] chains in most minerals take place through trans vertices of the octahedra, with one example of linkage through cis vertices; in nevadaite, the M – M linkage involves both trans and cis vertices, as does the chain in slavíkite . In most of these decorated chains, alternate tetrahedra along the chain occur either in a trans or a cis arrangement. In nevadaite and slavíkite, the tetrahedra are arranged in both trans and cis arrangements; the arrangements in these two minerals are geometrically distinct, however.

Nevada↗
USGS2003

Goldquarryite, a new Cd-bearing phosphate mineral from the Gold Quarry mine, Eureka County, Nevada

Goldquarryite, idealized formula CuCd2Al3(PO44F2(H2O)10(H2O 2, structure-derived formula (Cu0.70???0.30??1.00(Cd1.68Ca0.32??2.00Al3 (PO44F2(H2O)10[(H2O 1.60F0.40]??2.00, is triclinic, space group P1, with unit-cell parameters derived from crystal structure: a = 6.787(1), b = 9.082(2), c = 10.113(2) A??, ?? = 101.40(1)??, ?? = 104.27(1)??, ?? = 102.51(1)??, V = 568.7(3) A??3, a:b:c: = 0.7473:1:1.1135, Z = 1. The strongest seven reflections in the X-ray powder-diffraction pattern are [d(A??)(I)(hkl)]: 9.433(100)(001); 4.726(30)(002); 3.700(30)(022); 3.173(30b)(122, 113, 120, 003); 3.010(30)(122, 212); 2.896(30)(211); 2.820(50)(022). The mineral occurs on a single specimen collected from the 5,425-foot bench, Gold Quarry mine, Eureka County, Nevada, as isolated clusters of radiating sprays of crystals and as compact parallel crystal aggregates, which are both found on and between breccia fragments. Sprays and aggregates never exceed 3 mm in longest dimension and typically average about 0.5 mm in size. Goldquarryite is a late-stage supergene mineral associated with opal, carbonate-fluorapatite and hewettite, on a host rock composed principally of brecciated and hydrothermally rounded jasperoid fragments which have been lightly cemented by late-stage silicification. Individual euhedral crystals are acicular to bladed, elongate [100], with a length-to-width ratio of approximately 20:1; the maximum size is 1.5 mm but most crystals do not exceed 0.4 mm in length. Forms are {010}, {001} major and {100} very minor. The mineral is pleochroic; translucent (masses) to transparent (crystals); very pale blue to blue-gray (crystals) or blue (masses); with a white streak and a vitreous to glassy luster. Goldquarryite is brittle, lacks cleavage, has an irregular fracture, and is nonfluorescent; hardness (Mohs') is estimated at 3-4; measured density is 2.78(1) g/cm3 (sink-float techniques using methylene iodide-acetone mixtures), calculated density is 2.81 g/cm3 (for formula and unit-cell parameters derived from crystal structure). Optically, it is biaxial positive, ?? = 1.570, ?? = 1.573, ?? = 1.578; 2V (meas.) = ???30??, 2V (calc.) = 76??; dispersion r < v, strong. Average electron-microprobe analysis: K2O = 0.17, CuO = 5.33, CaO = 1.25, NiO = 0.23, ZnO = 0.05, CdO = 26.24, Al2O3 = 15.22, V2O3 = 0.05, P2O5 = 28.04, F = 3.63, H2O (calculated assuming stoichiometry) = [22.19], -O = F = -1.53, total = 100.87 weight %, corresponding to [(Cu0.66Ni0.03Zn0.01) ??0.70.

Mineralogical Record↗
USGS2002

Ordonezite from the Theodoso Soto Mine, Sapioris, Durango, Mexico: New data and structure refinement

A new occurrence of the rare mineral species ordonezite has been found at the Theodoso Soto tin mine, near Sapioris, Durango, Mexico. The average composition of the samples is (Zn 0.98 Fe 0.02 ) &Sigma;1.00 Sb 2.00 O 6 ; the core of the crystals is slightly richer in Fe than the rim. The mineral is uniaxial (+), with all n greater than 2.30 (n calc is 2.38 at 589 nm); D obs 6.66 g/cm 3 , D calc 6.67 g/cm 3 . It is isostructural with ferrotapiolite, with a 4.668(2), c 9.269(6) A (from powder-diffraction data), space group P4 2 /mnm, and is twinned on {103}. Its crystal structure, refined to R=4.1, wR=4.3% using 163 observed reflections, is fully cation-ordered.

Durango↗
USGS2000

Ruby and sapphire from Jegdalek, Afghanistan

This study provides detailed mining and gemological information on the Jegdalek deposit, in east-central Afghanistan, which is hosted by elongate beds of corundum-bearing marble. Some facet-grade ruby has been recovered, but most of the material consists of semitransparent pink sapphire of cabochon or carving quality. The most common internal features are dense concentrations of healed and nonhealed fracture planes and lamellar twin planes. Color zoning is common, and calcite, apatite, zircon, mica, iron sulfide minerals, graphite, rutile, aluminum hydroxide, and other minerals are also present in some samples. Although the reserves appear to be large, future potential will depend on the establishment of a stable government and the introduction of modern mining and exploration techniques.

Jegdalek deposit↗
USGS1999

Simmonsite, Na2LiAlF6, a new mineral from the Zapot amazonite-topazzinnwaldite pegmatite, Hawthorne, Nevada, U.S.A

Simmonsite, Na2LiAlF6, a new mineral of pegmatitic-hydrothermal origin, occurs in a late-stage breccia pipe structure that cuts the Zapot amazonite-topaz-zinnvvaldite pegmatite located in the Gillis Range, Mineral Co., Nevada, U.S.A. The mineral is intimately intergrown with cryolite, cryolithionite and trace elpasolite. A secondary assemblage of other alumino-fluoride minerals and a second generation of cryolithionite has formed from the primary assemblage. The mineral is monoclinic, P21 or P21/m, a = 7.5006(6) A??, b = 7.474(1) A??, c = 7.503(1) A??, ??= 90.847(9) ??, V=420.6(1) A??3, Z = 4. The four strongest diffraction maxima [d(A??), likl, I/I100] are (4.33, 111 and 111, 100); (1.877, 400 and 004, 90); (2.25, 13T, 113, 131 and 311, 70); and (2.65, 220, 202, 022, 60). Simmonsite is pale buff cream with white streak, somewhat greasy, translucent to transparent, Mohs hardness of 2.5-3, no distinct cleavage, subconchoidal fracture, no parting, not extremely brittle, Dm is 3.05(2) g/cm3, and Dc is 3.06(1) g/cm3. The mineral is biaxial, very nearly Isotropie, N is 1.359(1) for ?? = 589 nm, and birefringence is 0.0009. Electron microprobe analyses gave (wt%) Na = 23.4, Al = 13.9, F = 58.6, Li = 3.56 (calculated), with a total of 99.46. The empirical formula (based on 6 F atoms) is Na1.98Li1.00 ooAl|ooF6. The crystal structure was not solved, presumably because of unit-cell scale twinning, but similarities to the perovskite-type structure exist. The mineral is named for William B. Simmons, Professor of Mineralogy and Petrology, University of New Orleans, New Orleans.

American Mineralogist↗
USGS1999

The Zapot pegmatite mineral county

The Zapot pegmatite is currently being mined for mineral specimens (chiefly amazonite, topaz and smoky quartz in miarolitic cavities), for gemstones (topaz and smoky quartz) and for decorative rock (amazonite). The deposit is owned and operated by Harvey Gordon Minerals of Reno, Nevada, and is the only amazonite-topaz mining operation in the state. Thousands of specimens from this operation have reached the collector market.

Mineralogical Record↗
USGS1999

The chemistry, mineralogy, and petrology of the George Ashley Block pegmatite body

The George Ashley Block (GAB) is a rockslide block located in the Pala pegmatite district of Southern California. It is layered, asymmetric, pocket containing, and peraluminous. The GAB consists of quartz (42 vol%), Na-rich plagioclase (27%), potassium feldspar (24%), muscovite (7%), Mn-rich garnet (2%), biotite (1%), and a trace of tourmaline and gahnite. It contains only small amounts of the incompatible elements that characterize differentiated pegmatite bodies. P2O5, MnO, and F are present in amounts of < 1 wt% each; B, Be, Ce, Li, Nb, Nd, and Th are < 100 ppm each. More than 90% of the garnet grains in the GAB are zoned toward Mn-rich rims, and a symmetrical change in garnet-core composition occurs across the body. The mean X site contents for garnet (in at%) are 57% Fe, 40% Mn, 3.1% Mg, and 0.4% Ca. The Mn contents of garnet range from 30 to 55 at%; Fe contents vary inversely with Mn and range from about 66 to 43 at%. It is concluded that the bulk chemistry yields little information about fractionation, but the garnet, muscovite, and biotite mineral chemistry is more useful. There may have been two separate injections of magma to form the GAB.

American Mineralogist↗
USGS1998

Micas from the Pikes Peak batholith and its cogenetic granitic pegmatites, Colorado: Optical properties, composition, and correlation with pegmatite evolution

Optical properties are presented for 66 samples of mica covering the range from annite ??? biotite ??? zinnwaldite ??? ferroan lepidolite and ferroan muscovite from occurrences of granitic pegmatite (NYF type) throughout the Pikes Peak batholith (PPB) in Colorado. Chemical composition was determined for 34 of these samples. The optical data are correlated with composition, mode of occurrence, and relation to pegmatite paragenesis. Optical properties of the trioctahedral micas show a consistent trend of decreasing ?? index of refraction, from an average of 1.693 in annite of the host granite to 1.577 in zinnwaldite and ferroan lepidolite of the miarolitic cavities, which correlates with a progressively decreasing content of Fe. A comparison of optical and compositional data for micas from localities throughout the PPB indicates a variation in geochemical evolution among pegmatites of different districts, and between the Pikes Peak Granite and its late satellite plutons. Analyses of mica samples taken from cross-sections through individual pegmatites reveal a decrease in index of refraction and total iron that unambiguously document a progressive geochemical evolution within a given pegmatite. Such data, in addition to field evidence, indicate that micas enclosed within massive quartz are paragenetically older than those within miarolitic cavities; minerals within miarolitic cavities represent the final stages of primary crystallization. A general model of pegmatite paragenesis is proposed that hypothesizes formation of miarolitic cavities as a consequence of pegmatite configuration and inclination, as well as early crystallization of massive quartz that confines the silicate melt and volatile phase, resulting in closed-system crystallization with a concomitant increase in pressure, consequent episodic cavity-rupture events, and corresponding changes in mica composition.

Canadian Mineralogist↗
USGS1997

Geochemical characteristics and K-Ar ages of rare-metal bearing pegmatites from the Birimian of southeastern Ghana

The pegmatite-aplite rocks at Mankwadzi (Ejisimanku Hills) in southeastern Ghana are part of the pegmatite district that extends from Cape Coast to Winneba along the Atlantic coastline. The pegmatites are associated with the Cape Coast granite complex and were intruded during the waning phase of the Eburnian Orogeny (∼2.0 Ga). Three muscovite separates from pegmatite give KAr retention ages of 1909 ± 13 Ma , 1965 ± 13 Ma and 2019 ± 14 Ma. A biotite separate from granite yields a KAr age of 1907 ± 13 Ma. These ages are similar to KAr dates previously reported for the Cape Coast granites, indicating that the granites and pegmatites are coeval and probably genetically linked. The pegmatites are enriched in Li, Be, Nb and Sn and considerably impoverished in Rb, Th, Y and REEs. Microscopic examination of quartz from the pegmatites shows a large number of low salinity fluid inclusions that can be divided into two types: (1) one-phase liquid or gas-filled inclusions; and (2) two-phase liquid-vapour inclusions, with the vapour occupying 2–5% of the volume. The homogenisation temperature of the fluid inclusions clusters between 129 and 144°C. These homogenisation temperatures lead to an inferred entrapment temperature of ∼300°C at a pressure of ∼2.5 kbar, which is estimated for the metamorphism of host hornblende schists. The pegmatite fluid inclusions are interpreted as being secondary to the quartz hosts.

Journal of African Earth Sciences↗
USGS1997

The role of diffusion-controlled oscillatory nucleation in the formation of line rock in pegmatite-aplite dikes

The George Ashley Block (GAB), located in the Pala Pegmatite District, San Diego County, California, is a composite pegmatite–aplite dike of 8 m thickness displaying striking mineralogical layering in the aplite portion of the dike, referred to as line rock. Rhythmic layering is characterized by garnet-rich bands alternating with albite–quartz–muscovite-rich bands. Cumulus textures are notably absent from the layered portion of the dike. Elongated quartz megacrysts are oriented perpendicular to the garnet-rich layers and poikilitically include garnet, albite, and muscovite. Calculated crystal-free magma viscosity with 3% H 2 O is 10 6.2 Pa s and the calculated settling velocity for garnet is 0.51 cm/year. Conductive cooling calculations based on emplacement of a 650°C dike into 150°C fractured gabbroic country rock at 1.5 kbar, and accounting for latent heat of crystallization, demonstrate that the line rock portion of the dike cools to 550°C in about 1 year. Crystal size distribution studies also suggest very rapid nucleation and crystallization. Diffusion-controlled gel crystallization experiments yield textures virtually identical to those observed in the layered aplite, including rhythmic banding, colloform layering, and band discontinuities. Thus, observed textures and calculated magmatic parameters suggest that mineralogical layering in the GAB results from an in situ diffusion-controlled process of oscillatory nucleation and crystallization. We propose that any event that promotes strong undercooling has the potential to initiate rapid heterogeneous nucleation and oscillatory crystal growth, leading to the development of a layer of excluded components in front of the crystallization front, and the formation of line rock.

Journal of Petrology↗
USGS1997

Incorporation of rare earth elements in titanite: Stabilization of the A2/a dimorph by creation of antiphase boundaries

The atomic arrangement of a natural rare-earth-rich titanite and two synthetic rare-earth-doped titanites have been refined in space group A2/a, and the atomic arrangement of an undoped P21/a synthetic titanite was also refined for comparison. Previous work has shown that titanite possesses a domain structure, with domains formed of like-displaced Ti atoms in the [100] octahedral chains. P21/a titanite results when the crystal is formed of a single domain, but as Ti-reversal sites occur in the octahedral chain the apparent A2/a structure results from the average of antiphase domains. Antiphase boundaries occur at O1, which is alternately overbonded or underbonded at the boundaries, depending on the displacement of the neighboring Ti atoms. Type 2 antiphase boundaries exist where two Ti atoms are displaced away from the intervening O1 atom and are energetically unfavorable because of underbonding of that O1 atom. However, substitution of a trivalent rare earth element in the adjacent Ca2+ site relieves that underbonding, favoring the creation of type 2 antiphase boundaries and stabilization of the A2/a dimorph. The results of high-precision crystal structure analyses demonstrate that rare earth substituents for Ca stabilize the A2/a dimorph at lower substitution levels than required for octahedral substitutions.

American Mineralogist↗
USGS1997

The chemical evolution and paragenesis of uranium minerals from the ruggles and palermo granitic pegmatites, New Hampshire

A study of the chemical evolution and paragenesis of the uranium minerals at the Palermo No. 1 and Ruggles granitic pegmatites, Grafton County, New Hampshire, revealed four stages of secondary mineralization. A total of eight uranium minerals were identified in the four stages. The first stage is a mixture of uranyl oxide hydroxide-hydrates represented by mineral "A", which surrounds and replaces a uraninite core. The second stage is a carbonate stage found only at the Palermo No. 1 pegmatite, and is represented by rutherfordine. The third stage is represented by uranyl silicates. At the Palermo No. 1 pegmatite, this stage consists of ??-uranophane, and at the Ruggles pegmatite, it consists of soddyite and ??-uranophane. A final fourth stage is a phosphate stage represented by phosphuranylite and meta-autunite I. The first three stages of mineralization developed from hydrothermal and meteoric processes. With dropping temperatures, hydrothermal fluids reached meteoric temperatures and acquired the characteristics of meteoric water. The pH shifted from acidic (pH less than about 6 at 100??C) to alkaline (pH > 7 at 25??C). Since mineral "A" contains hydroxyl and a low amount of molecular water, it probably formed at a temperature greater than 100??C in the acidic environment. After the first stage, the hydrothermal fluids likely reached the temperatures of meteoric water. The initial pH of the meteoric water was acidic (pH less than about 6 at 25??C) and then slowly shifted to alkaline. The mineralizing fluids became oversaturated in CO3, Ca, K, and Si. Uraninite and mineral "A" became unstable and were replaced by rutherfordine and uranyl silicates. The fourth or phosphate stage developed from the introduction of groundwater. The uranyl phosphate minerals precipitated from an acidic fluid (pH < 7 at 25??C) that was oversaturated with Ca, K, U, and P.

Canadian Mineralogist↗
USGS1997

Additional studies on mixed uranyl oxide-hydroxide hydrate alteration products of uraninite from the palermo and ruggles granitic pegmatites, grafton county, New Hampshire

Additional studies on an incompletely characterized secondary uranium "mineral" from the Ruggles and Palermo granitic pegmatites, New Hampshire, referred to as mineral "A" by Frondel (1956), reveal a mixture of schoepite-group minerals and related uranyl oxide-hydroxide hydrated compounds. A composite chemical analysis yielded (in wt.%): PbO 4.85 (EMP), UO3 83.5 (EMP), BaO 0.675 (av. of EMP and ICP), CaO 0.167 (av. of EMP and ICP), K2O 2.455 (av. of EMP and ICP), SrO 0.21 (ICP), ThO2 0.85 (ICP), H2O 6.9, ??99.61. Powder-diffraction X-ray studies indicate a close resemblance in patterns between mineral "A" and several uranyl oxide-hydroxide hydrated minerals, including the schoepite family of minerals and UO2(OH)2. The powder-diffraction data for mineral "A" are most similar to those for synthetic UO2.86??1.5H2O and UO2(OH)2, but other phases are likely present as well. TGA analysis of both mineral "A" and metaschoepite show similar weight-loss and first derivative curves. The dominant losses are at 100??C, with secondary events at 400?? and 600??C. IR spectra show the presence of (OH) and H2O. Uraninite from both pegmatites, analyzed by LAM-ICP-MS, shows the presence of Th, Pb, K and Ca.

Canadian Mineralogist↗
USGS1996

Li- and F-bearing alkali amphibole from granitic pegmatite at Hurricane Mountain, Carroll County, New Hampshire

At Hurricane Mountain, Carroll County, New Hampshire, bodies of granitic pegmatite in riebeckite granite contain large (up to 10 cm long and 2 cm across) primary crystals of Li-bearing fluor-arfvedsonite in miarolitic cavities, grading to euhedral Li- and F-poor arfvedsonite. Fine-grained, fibrous, light blue-gray riebeckite occurs as a late-stage hydrothermal filling in the miarolitic cavities. The early, Li-rich, fluor-arfvedsonite has: a 9.836(5), b 17.997(7), c 5.316(4) A??, ?? 103.735(4)??, V 914.20(6) A??3; Z = 2, Dmeas. 3.34 g/cm3, Dcalc. 3.353 g/cm3; biaxial (-), 2Vmeas. 44(1)??, 2Vcalc. 46??; ?? 1.681(2), ?? 1.692(2), ?? 1.694(2), inclined dispersion, r > v; X ??? c -7??, Y = b, Z ??? a +7??; X dark blue, Y lavender gray, Z pale yellowish brown; X > Y > Z; X is opaque at 0.03 mm thickness. A structural formula, on the basis of 24 (O,OH,F) atoms is: (Na0.86K0.25)Na2(Fe2+2.54Fe3+1.485Mn0.10Zn 0.02Li0.49Ti0.07)(Si7.71Al 0.07)O22(F1.34OH0.63). Arfvedsonite within the miarolitic cavities contains less Li and F than that of the earlier generation, and the still later riebeckite contains only 0.09 wt.% Li2O and 0.3 wt.% F. The Fe3+:Fe2+ ratio of the early Li-bearing fluor-arfvedsonite and that of the euhedral arfvedsonite crystals within miarolitic cavities is 0.58. The late, fibrous, cavity-filling riebeckite has an Fe3+:Fe2+ ratio of 0.99. The total iron content of the three amphiboles increases with continued crystallization. These amphiboles are products of peralkaline pegmatites locally derived from peralkaline granite.

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