Hani Khoury

Origin of magnesium clays from the Amargosa Desert, Nevada

Deposits of sepiolite, trioctahedral smectite (mixed-layer kerolite/stevensite), calcite, and dolomite, found in the Amargosa Flat and Ash Meadows areas of the Amargosa Desert were formed by precipitation from nonsaline solutions. This mode of origin is indicated by crystal growth patterns, by the low Al content for the deposits, and by the absence of volcanoclastic textures. Evidence for low salinity is found in the isotopic compositions for the minerals, in the lack of abundant soluble salts in the deposits, and in the crystal habits of the dolomite. In addition, calculations show that modern spring water in the area can precipitate sepiolite, dolomite, and calcite following only minor evaporative concentration and equilibration with atmospheric CO2. However, precipitation of mixed-layer kerolite/stevensite may require a more saline environment. Mineral precipitation probably occurred during a pluvial period in shallow lakes or swamps fed by spring water from Paleozoic carbonate aquifers.РезюмеРезюме—Отложения сепиолита, трехоктаэдрического смектита (смешанно-слойного керолита/стевенсита), кальцита, и доломита, найденные в районах Амаргоской низменности и пепловых лугов Амаргоской пустыни, были образованы путем осаждения из несоленых растворов. На этот способ происхождения указывают структуры роста кристаллов, низкое содержание Аl в отло-жениях ш отсутствие вулканокластических текстур. Свидетельством низкой солености являются изотопные составы минералов, отсутствие обильных растворимых солей в отложениях и кристал-лические черты доломита. Кроме того, расчеты показывают, что современная источниковая вода в районе может осаждать сепиолит, доломит и кальцит после незначительной испарительной кон-центрации и равновесия с атмосферическим CO2. Однако, осаждение смешанно-слойного керо-лита/стевенсита может потребовать более соленой среды. Минеральные осаждения, вероятно, выступили в течение плювиального периода в мелких озерах или топях, питаемых источниковой водой из палеозойских карбонатных водоносных пластов. [Е.С.]ResümeeAblagerungen von Sepiolith, trioktaedrischem Smektit (Wechsellagerung Kerolit/Stevensit), Calcit, und Dolomit, die in den Gebieten Amargosa Flat und Ash Meadows der Amargosa Wüste gefunden werden, bildeten sich durch Ausfallung aus nicht-salinen Lösungen. Diese Entstehungsart ergibt sich aus der Art des Kristallwachstums, dem niedrigen Al-Gehalt der Ablagerungen und durch das Fehlen von vulkanoklastischen Strukturen. Der Beweis für eine niedrige Salinität ergibt sich aus den einheitlichen Zusammensetzungen der Minerale, aus dem Fehlen überschüssiger löslicher Salze in den Ablagerungen und aus den Arten des Kristallhabitus von Dolomit. Außerdem zeigen Berechnungen, daß aus rezentem Quellwasser dieses Gebietes Sepiolith, Dolomit und Calcit ausfallen kann, was nur von einer geringen Konzentrierung durch Evaporation und von der Gleichgewichtseinstellung mit dem CO2 der Luft abhängt. Die Ausfallung der Wechsellagerung Kerolit/Stevensit könnte jedoch höher saline Bedingungen erfordern. Diese Mineralausfällung geschah wahrscheinlich während einer pluvialen Periode in seichten Seen odor Mooren, die von Quellwasser aus paläozoischen, karbonathaltigen wasserführenden Schichten gespeist wurden. [U.W.]RésuméDes dépôts de sepiolite, de smectite trioctaèdre (kérolite/stevensite à couches mélangées), de calcite, et de dolomite, trouvés dans les régions de l’Amargosa Fiat et d’Ash Meadows du désert d’Amargosa ont été formés par la précipitation de solutions non-salines. Ce mode d’origine est indiqué par les dessins de croissance cristallographique, par le bas contenu en Al des dépôts, et par l’absence de textures volcanoclastiques. L’évidence pour la basse salinité est trouvée dans les compositions isotopiques pour les minéraux, dans le manque d’abondants sels solubles dans les dépôts, et dans les habitudes cristallographiques de la dolomite. De plus, des calculs montrent que de l’eau de source moderne dans la région peut précipiter la sépiolite, la dolomite, et la calcite suivant une concentration evaporative mineure et l’équilibration avec du CO2 atmosphérique. La précipitation de kérolite/stevensite à couches mélangées peut cependant exiger un environement plus salin. La précipitation des minéraux s’est probablement passée pendant une période pluviale dans des lacs peu profonds ou dans des marais nourris d’eau de source provenant des aquifères carbonates paléozoiques. [D.J.]

A natural analogue of high pH cement pore waters from the Maqarin area of northern Jordan. I: introduction to the site

Abstract The highly alkaline springs of the Maqarin area of northern Jordan are currently under examination as part of an international project testing the models used to analyse the safety of repositories for low and intermediate level radioactive waste (L/ILW). The Maqarin area contains a rock-groundwater system which is an ideal natural analogue of a concrete-filled L/ILW repository emplaced in a sedimentary host rock. The high pH (12.5) groundwaters at this site are the product of interaction with naturally occurring cement minerals and not of the alteration of ultramafic minerals. Stable isotope data for the hyperalkaline groundwaters lie below both the local meteoric water line and the eastern Mediterranean water line. At least part of the shift appears to be the result of groundwater interaction with the cement minerals. This paper introduces the site of the natural analogue study and, in presenting novel data on the chemistry and stable isotopic signature of the groundwater, provides background information which is used in a companion paper (Alexander et al., 1992) on testing the predictive capabilities of geochemical thermodynamic codes (and their associated databases) which will be utilised as part of the safety assessment of a L/ILW repository.

The influence of using Jordanian natural zeolite on the adsorption, physical, and mechanical properties of geopolymers products

Geopolymers consist of an amorphous, three-dimensional structure resulting from the polymerization of aluminosilicate monomers that result from dissolution of kaolin in an alkaline solution at temperatures around 80 degrees C. One potential use of geopolymers is as Portland cement replacement. It will be of great importance to provide a geopolymer with suitable mechanical properties for the purpose of water storage and high adsorption capacity towards pollutants. The aim of this work is to investigate the effect of using Jordanian zeolitic tuff as filler on the mechanical performance and on the adsorption capacity of the geopolymers products. Jordanian zeolitic tuff is inexpensive and is known to have high adsorption capacity. The results confirmed that this natural zeolitic tuff can be used as a filler of stable geopolymers with high mechanical properties and high adsorption capacity towards methylene blue and Cu(II) ions. The XRD measurements showed that the phillipsite peaks (major mineral constituent of Jordanian zeolite) were disappeared upon geopolymerization. The zeolite-based geopolymers revealed high compressive strength compared to reference geopolymers that employ sand as filler. Adsorption experiments showed that among different geopolymers prepared, the zeolite-based geopolymers have the highest adsorption capacity towards methylene blue and copper(II) ions.

Mixed-layer kerolite/stevensite from the Amargosa Desert, Nevada.

Mixed-layer clays composed of randomly interstratified kerolite/stevensite occur as lake and/or spring deposits of probable Pliocene and Pleistocene age in the Amargosa Desert of southern Nevada, U.S.A. The percentage of expandable layers of these clays, determined from computer-simulated X-ray diffractograms, ranges from almost 0 to about 80%. This range in expandabilities most likely results from differences in solution chemistry and/or temperature at the time of formation. An average structural formula for the purest clay (sample P-7), a clay with about 70% expandable layers, is:

Recarbonation of metamorphosed marls, Jordan

{\left[ {\left( {M{g_{2,72}}A{l_{0,07}}F{e_{0.03}}L{i_{0.09}}} \right)\left( {S{i_{3.96}}A{l_{0.04}}} \right){O_{10}}{{\left( {OH} \right)}_2}} \right]^{ - 0.21}}{\left[ {X_{0.21}^ + } \right]^{ + 0.21}}.

The Maqarin (Jordan) natural analogue for 14C attenuation in cementitious barriers

The data suggest that talc, kerolite, and stevensite form a continuous structural series based on layer charge.РезюмеРезюме—Смешано-слойные глины, составленные из случайно внутринапластованного керолита/стевенсита залегают как озерные и/или источниковые осадки, вероятно, плиоценовой и плейсто-ценовой эпохи на пустыни Амаргоса в южной Неваде, С.Ш. Процентное отношение расширя-ющихся слоев в этих глинах, определенное путем компьютерномоделированных рентгеновских дифрактограммов, находится в диапазоне от 0 до 80%. Этот диапазон, вероятно, есть результатом различной химии растворов и/или разных температур во время формирования. Средняя струк-турная формула наиболее чистого образца глины (Р-7) с около 70% растирающихся слоев есть:

Intermediate members of the lime-monteponite solid solutions (Ca1−xCdxO, x = 0.36–0.55): Discovery in natural occurrence

{\left[ {\left( {M{g_{2,72}}A{l_{0,07}}F{e_{0.03}}L{i_{0.09}}} \right)\left( {S{i_{3.96}}A{l_{0.04}}} \right){O_{10}}{{\left( {OH} \right)}_2}} \right]^{ - 0.21}}{\left[ {X_{0.21}^ + } \right]^{ + 0.21}}.