Authigenic Silicate Minerals in Searles Lake, California

Abstract--Experimental alteration of obsidian was performed in 0.001 to 0.5 N NaOH and KOH solutions at 150 and 200 ~ for 1 to 30 d. The products were examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). Changes in chemical composition and pH value of solutions during the reactions were also measured. As the pH of reacting solutions was increased, smectite, phillipsite and rhodesite crystallized progressively in NaOH solutions, while smectite, merlinoite and sanidine grew successively in KOH solutions. In addition, a small amount of less-soluble, poorly ordered boehmite was present as products of all the experiments. Smectite mainly appeared at slightly high pH, Si/A1 and Na/K conditions, whereas rhodesite should be produced in extremely high pH, Na/K and Si/A1 conditions. Sanidine was also formed in conditions of very high pH and Si/A1 and very low Na/K. In intermediate conditions of pH and Si/A1, crystallization of phillipsite was stimulated in solutions of Na/K > 10, while formation of merlinoite was favored in conditions of Na/K < 1.

Section: Discussionmentioning

confidence: 99%

Experimental Study on the Formation of Zeolites from Obsidian by Interaction with NaOH and KOH Solutions at 150 and 200 °C

Kawano

1997

“…Phillipsite has been reported in all of these lake sediments (Hay and Moiola, 1963;Hay, 1964;Hay, 1966), but the exceptionally high potassium concentration (Na/K = 7.2-13.1) and high pH (9.1-9.5) of the Searles Lake brines has led to the formation of K-feldspar as the dominant authigenic silicate at Searles Lake. Based on the above discussion, the chemistry of the Searles Lake brines would seem likely to favor the formation of merlinoite.…”

Section: Discussion and Geologic Applicationmentioning

confidence: 99%

Synthesis and Characterization of Zeolites in the System Na₂O-K₂O-Al₂O₃-SiO₂-H₂O

Donahoe

Liou

Guldman

1984

Abstraet--Zeolites having the structures of phillipsite, merlinoite, and gobbinsite were synthesized from clear solutions at 80~ in the system Na20-K20-Ai203-SiO2-H20 and their morphologies, cell parameters, and compositions determined. At 3.5 M silica concentration, the formation of merlinoite (synthetic zeolite W) is favored over the formation of phillipsite (synthetic zeolite ZK-19) by solution conditions of high pH (> 13.6) and low Na/(Na + K) ratios (<0.5).Using the information obtained from the synthesis experiments, the presence ofmerlinoite was predicted in sediments from Searles Lake, a saline, alkaline lake in California with ideal physiochemical conditions for its formation. Merlinoite was subsequently discovered to occur in tuffaceous sediments as part of an authigenic silicate zonation pattern from phillipsite -phillipsite + merlinoite ~ merlinoite ~ K-feldspar with increasing depth. Because of the close similarities in the physical properties of phillipsite and merlinoite, merlinoite may be much more common as an authigenic mineral than is currently realized.

“…It is noted for its variety of saline minerals and for its alkaline brines that are ultilized for the commercial extraction of K, B, Li, and Na2CO3. Earlier work on drill cores from the upper 267 m of sediments showed that silicic tephra is altered to phillipsite at higher levels and to K-feldspar and searlesite (NaBSi2Or' HzO) at lower levels (Hay and Moiola, 1963). The K-feldspar was believed to have formed from a phillipsite precursor (Hay, 1966), a reaction which Sheppard and Gude (1968) demonstrated elsewhere.…”

Section: Introductionmentioning

confidence: 99%

Diagenetic Alteration of Silicic Ash in Searles Lake, California

Hay

Guldman

1987

Abstract--Ash layers from Searles Lake, California, were sampled in core of drill hole KM-3, which penetrated 693 m of lacustrine sediment deposited in a playa-lake complex over the past 3.2 my. Lake water changed from moderately saline and slightly alkaline (pH ~7.5) to highly saline 2.04 my ago and to highly saline and alkaline (pH -9.5) 1.28 my ago. As a result of brines flushing downward, the upper 291 m of sediment, spanning the past 1.28 my, contain highly saline, alkaline pore fluid. Silicic ash layers in contact with highly saline, alkaline pore fluid were first altered to phillipsite and merlinoite and then to K-feldspar and searlesite. The transformation of phillipsite and/or merlinoite to K-feldspar required more than 45,000 years and was largely completed in 140,000 years. Tephra layers in contact with moderately saline, slightly alkaline pore fluid vary from uncemented vitric ash containing minor smectite to bentonites in which glass is wholly altered to smectite, clinoptilolite, analcime, and opal. Layers with much fine tephra are more altered than the coarser, better-sorted layers. Alteration is attributed to hydrolysis in essentially a closed hydrologic system, in which the alteration of glass to smectite raised the pH, as~o2, and (Na + + K+)/H + activity ratio to the level where clinoptilolite formed. Some diffusion and/ or fluid flow is, however, indicated by the loss of SiOz during the alteration of ash layers to smectite and by anhydrite deposited during and after clinoptilolite in some tuffaceous sandstones.