Browsing by Author "Colchester, DM"

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    Exceptional datolite crystals from Albion Park, New South Wales: morphology, chemistry and likely origin
    (Mineralogical Society of Victoria, 2018) Graham, IT; Colchester, DM; Cendón, DI; Lay, A; Hergt, JM; Greig, A; Larsen, JR
    Large, well-formed, semi-transparent yellow–green crystals up to 5.6 cm were found in cavities within the Late Permian Bumbo Latite Member of the Gerringong Volcanics in the now abandoned Cleary Brothers Quarry, Albion Park, New South Wales. Although labelled by the collector as calcite, these were later identified as datolite, with two distinct habits, occurring on a matrix of crystallized quartz and prehnite. The datolite contains very low concentrations of elements other than the essential calcium, silicon, oxygen and boron. Its distinctive chondrite-normalized, positive europium anomaly, when compared with datolite data from elsewhere, suggests crystallization from postdiagenetic hydrothermal fluids in the temperature range of 200–250°C. These datolite crystals are the finest ever found in Australia and rank highly with those found elsewhere in the world. © 2018 Mineralogical Society of Victoria
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    Sulfate and phosphate speleothems at Jenolan Caves, New South Wales, Australia
    (Slovenian Academy of Sciences and Arts and ZRC SAZU Karst Research Institute, 2011-09-01) Pogson, RE; Osborne, RAL; Colchester, DM; Cendón, DI
    Sulfate and phosphate deposits at Jenolan Caves occur in a variety of forms and compositions including crusts, ‘flowers’ and fibrous masses of gypsum (selenite), and clusters of boss-like speleothems (potatoes) of ardealite (calcium sulphate, phosphate hydrate) with associated gypsum. This boss-like morphology of ardealite does not appear to have been previously described in the literature and this is the first report of ardealite in New South Wales. Gypsum var. selenite occurs in close association with pyrite-bearing palaeokarst, while the ardealite gypsum association appears to relate to deposits of mineralised bat guano. Isotope studies confirm that the two gypsum suites have separate sources of sulfur, one from the weathering of pyrite (-1.4 to +4.9 δ34S) for gypsum (selenite) and the other from alteration of bat guano (+11.4 to +12.9 δ34S) for the ardealite and gypsum crusts. © 2011 The Authors