Journal Article Extrusive Carbonatites from the Uyaynah Area, United Arab Emirates Get access A. R. WOOLLEY, A. R. WOOLLEY 1Department of Mineralogy, British Museum (Natural History)Cromwell Road, London S W7, 5BD, UK Search for other works by this author on: Oxford Academic Google Scholar M. W. C. BARR, M. W. C. BARR 2Hunting Technical Services Limited, Thamesfield HouseBoundary Way, Hemel Hempstead, Hertfordshire HP2 7SR, UK Search for other works by this author on: Oxford Academic Google Scholar V. K. DIN, V. K. DIN 1Department of Mineralogy, British Museum (Natural History)Cromwell Road, London S W7, 5BD, UK Search for other works by this author on: Oxford Academic Google Scholar G. C. JONES, G. C. JONES 1Department of Mineralogy, British Museum (Natural History)Cromwell Road, London S W7, 5BD, UK Search for other works by this author on: Oxford Academic Google Scholar F. WALL, F. WALL 1Department of Mineralogy, British Museum (Natural History)Cromwell Road, London S W7, 5BD, UK Search for other works by this author on: Oxford Academic Google Scholar C. T. WILLIAMS C. T. WILLIAMS 1Department of Mineralogy, British Museum (Natural History)Cromwell Road, London S W7, 5BD, UK Search for other works by this author on: Oxford Academic Google Scholar Journal of Petrology, Volume 32, Issue 6, December 1991, Pages 1143–1167, https://doi.org/10.1093/petrology/32.6.1143 Published: 01 December 1991 Article history Received: 25 September 1990 Accepted: 29 March 1991 Published: 01 December 1991
Abstract Barstowite, ideally 3PbCl 2 .PbCO 3 .H 2 O is a new mineral from a lead-antimony vein at the south-western end of Bounds Cliff, St Endellion, Cornwall. It occurs as very small (0.2–0.5 mm) subparallel elongate intergrown crystals which form aggregates (up to 3 mm) containing minor inclusions of galena and jamesonite. Other associated minerals are quartz, dolomite, phosgenite, cerussite, sphalerite, pyrite and chalcopyrite. Barstowite is colourless to white and is transparent with an adamantine lustre and white streak. It is brittle, has an imperfect prismatic cleavage, and an uneven fracture. Low reflecting, barstowite has a moderate bireflectance from grey to dark grey in hue and weak to moderate anisotropy. Internal reflections (colourless) are abundant. Measured reflectance values in air and oil are tabulated. Colour values relative to the CIE illuminant C for R 1 and R 2 in air respectively are: Y % 12.9, 13.3; λ d 477, 476; P e % 3.5, 3.7. VHN 100 111 (range 108–117); calculated Mohs hardness is 3. Infrared spectra of barstowite, phosgenite and cerussite are compared. X-ray studies show that barstowite is monoclinic with space group P 2 1 / m and a 4.218(2), b 9.180(2), c 16.673(4) Å, β 91.49(3)°. It has a cell volume of 645.38 Å 3 with Z = 2. D calc . is 5.76 g/cm 3 , D meas . is 5.71 g/cm 3 . The strongest six lines of the X-ray powder pattern are [ d in Å (I) (hkl)] 4.02 (10) (022); 2.296(8) (040; ; 106); 2.377(6) (007; 026); 4.16(5) (004); 2.108(4) (200); 3.79(3) (014). The name is for the late Richard William Barstow, the Cornish mineral dealer.
Kap Edvard Holm, near Kangerdlugssuaq, forms part of one of the six Tertiary igneous centres of southern East Greenland. The plutonic rocks are mainly cumulate gabbros but there are several syenite masses, together with some minor granophyres and other acid rocks. The larger syenites - Kap Boswell, Kap Deichmann, and Hutchinson Gletscher I - are intruded as conical masses into the gabbros with an intermediate ring of igneous breccia. The petrography, mineralogy, and bulk chemistry of the rocks are reported. The syenites are generally nordmarkitic, containing hedenbergite and aegirine-augite, and amphiboles ranging from hastingsite, ferroedenite, and ferrorichterite (katophorite) to arfvedsonite, while aenigmatite is quite common in the Kap Boswell and Barberkniven syenites and veins. Many rock and mineral analyses are given. An estimate of the composition of the parent magma gives a nordmarkitic liquid very close to that of the main peripheral intrusions at Kangerdlugssuaq and also to the quartz trachytic late differentiate of the Azores alkali basalt. This agrees with the authors' earlier suggestion that all the syenite masses were most probably the products of a quartz trachyte magma, fractionated in the case of the main intrusion to yield the range of rock types occurring there, and itself produced by differentiation of an alkali basalt magma such as yielded some of the many dykes present in the region. An alternative explanation, proposed by Brooks & Gill (1982), that the main intrusion derived from the reaction of a foyaitic magma, fractionated from a nephelinitic parent, with the enclosing gneisses and basalts, could not have been repeated so exactly throughout the minor peripheral intrusions at Kangerdlugssuaq and again at Kap Edvard Holm.
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Abstract Sweetite, naturally occurring Zn(OH) 2 with tetragonal symmetry, has been found at Milltown, near Ashover, Derbyshire. It occurs as colourless or whitish bipyramids up to 1 mm in size scattered over the surface of colourless fluorite cubes. The cell dimensions are α 8,222 and c 14.34Å with Z = 20. The strongest lines of the X-ray powder pattern are ( d, I, hkl ): 4.53 37 (112); 3.572 60 (004,202,211); 2.922 100 (213,220); 2.708 18 (105,204); 2.257 17 (224,215,321); 1.840 11 (226,420,413); 1.764 24 (316). Sweetite is uniaxial negative, ω 1.635, ɛ 1.628. D meas is close to 3.33 and D calc 3.41. Chemical analysis gave 84.3% ZnO and 17.0% H 2 O, while theoretical figures for Zn(OH) 2 are 81.9 and 18.1% respectively.
Abstract— The known encounter velocity (6.1 kms −1 ) and particle incidence angle (perpendicular) between the Stardust spacecraft and the dust emanating from the nucleus of comet Wild‐2 fall within a range that allows simulation in laboratory light‐gas gun (LGG) experiments designed to validate analytical methods for the interpretation of dust impacts on the aluminum foil components of the Stardust collector. Buckshot of a wide size, shape, and density range of mineral, glass, polymer, and metal grains, have been fired to impact perpendicularly on samples of Stardust Al 1100 foil, tightly wrapped onto aluminum alloy plate as an analogue of foil on the spacecraft collector. We have not yet been able to produce laboratory impacts by projectiles with weak and porous aggregate structure, as may occur in some cometary dust grains. In this report we present information on crater gross morphology and its dependence on particle size and density, the pre‐existing major‐ and trace‐element composition of the foil, geometrical issues for energy dispersive X‐ray analysis of the impact residues in scanning electron microscopes, and the modification of dust chemical composition during creation of impact craters as revealed by analytical transmission electron microscopy. Together, these observations help to underpin the interpretation of size, density, and composition for particles impacted on the Stardust aluminum foils.
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