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Geochemical Characteristics and Expansion Properties of a Highly Potassic Perlitic Rhyolite from Lopburi, Thailand
Author(s) -
Saisuttichai Darunee,
Manning David A. C.
Publication year - 2007
Publication title -
resource geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 43
eISSN - 1751-3928
pISSN - 1344-1698
DOI - 10.1111/j.1751-3928.2007.00024.x
Subject(s) - electron microprobe , rhyolite , perlite , geology , mineralogy , empa , nuclear chemistry , geochemistry , volcanic rock , chemistry , materials science , volcano , metallurgy
Miocene volcanic rocks from northeast of Lopburi, Thailand, include a suite of highly potassic (<6.3% K 2 O) perlitic rhyolites that are similar chemically to rhyolites from Sardinia (which are also perlitic) and Vulcano. Electron microprobe analysis using a defocussed beam has shown that glass compositions contain up to 12.9% K 2 O (0.9% Na 2 O), and within the same samples spherulites are enriched in Na 2 O (<6.2%) and depleted in K 2 O (2.1%). The perlitic rhyolites contain up to 4% water of meteoric origin; from Fourier transform infra‐red spectroscopy data, expansion on heating involves a reduction in both hydroxyl and molecular water contents. When expanded using a laboratory test furnace, specific gravities as low as 26 kg/m 3 have been achieved for a 0.15–0.3‐mm feed size fraction (reference perlite ores from Milos and Sardinia gave 47 and 33 kg/m 3 , respectively), and 10 kg/m 3 for a 0.5–1‐mm fraction separated after expansion. Expansion involves the loss of fluorine from the perlite, presumably as HF; unexpanded perlite contains 90–550 mg/kg F, which is reduced on expansion by 4–65%. Water‐soluble fluorine after expansion is increased by a factor of 10 up to 3.3 mg/kg. Expansion also increases the availability of K to plants by a factor of up to 6, with a maximum available K content of 1245 mg K/kg perlite. This contrasts markedly with the chemically inert character of other, commercial, perlites, suggesting that the distinctive K‐enrichment of the perlitic rhyolite has given a raw material capable of generating products with nutritional functionality for plant growers.