Potassium Mica Research Articles

Synthesis of Arc-Derived DSDP (ODP) Modal Sand Compositions Using Multivariate Analyses: ABSTRACT

Sands derived from Quaternary and late Tertiary arc systems can be directly correlated with the tectonic setting of the marine basin in which they were deposited (trench, arc-trench gap, back arc, etc.), adjacent arc type continental margin versus intraoceanic; dissected versus undissected), and degree of arc/basin development at the time of deposition. Rigorous compositional classifications of these sediments are useful in interpreting tectonic setting of ancient sandstones of unknown or speculative origin. Representative arc-related sand samples from DSDP (ODP) sites form the basis of this investigation; regions sampled include the Mariana, Japan, Aleutian, North American, Middle American, Southwestern Pacific, Caribbean, and Mediterranean arc-related basins. Petrographic data were uniformly gathered using the Gazzi-Dickinson point-counting method. Modal sand compositions for each arc are unique, but marked differences along certain arc systems reflect the variable tectonic history of individual arc segments. Quartzo-feldspathic sands from the Mexican segment of the Middle American trench system sharply contrast with volcanic-rich sands from the Central American segment; more subtle changes occur along the sands from the Central American segment; more subtle changes occur along the Japan and North American arc systems. In general, multivariate analyses of petrographic data indicate (1) modal compositions of sands from magmatic-arc settingsmore » can be subdivided into intraoceanic arcs, continental arcs, and intraoceanic arcs with continental influence and (2) the percentage of continental components including potassium feldspar, quartz, mica, and sedimentary and metamorphic lithic grains increases toward continental margins. This synthesis represents the most complete study of modern arc sand compositions and provides information essential to studies of ancient arc-related sandstones.« less

Lithium in the interlayer space of synthetic trioctahedral micas

This paper gives several new and strong arguments in favour of the possibility of fixation of anhydrous lithium in the interlayer space of trioctahedral potassium micas. From the chemical viewpoint Li + can replace K +, but is located out of the alkaline cation site; it enters pseudo-octahedral cavities limited by the triangular bases of two aluminous tetrahedra of two consecutive sheets. The solubility limit of Li + in the interlayer is a function of the Al IV content of the mica. It is given by the relation ( Li Li + K) max = 2[( Al Si + Al) IV ] 2 . In both micas investigated — phlogopite, KMg 3(Si 3Al)O 10(OH) 2, and eastonite, K(Mg 2.5Al 1.5)(Si 2.5Al 1.5)O 10(OH) 2 — there is a remarkable agreement between the calculated values of the solubility limits and those measured by exchange reactions with hydrothermal solutions, at 600°C, 2 kbar. In high-Al micas, the interlayer Li content can be very important, with about one-third of K + replaced by Li +. The fixation of Li + according to this model provokes a strong flattening of the interlayer (strong decrease of the reticular distance d 005) and a slight increase of the reticular distance d 060. Infra-red (IR) absorption spectrometry shows that vacant K + sites are created when Li + enters the interlayer; one observes low-frequency OH stretching bands attributed to OH dipoles lying towards these empty sites. Fixation of Li + does not provoke any modification of the IR spectra in the region 1200-300 cm −1, indicating that Li + is really out of the sheet. For both cell dimensions and IR spectra, a comparison is made with “ordinary” lepidolites, having Li + in the octahedral sheet; it provides a guide for the distinction between the two species of Li-bearing micas.

The (?) mid Triassic volcanic rocks of Lakonia, Greece

SummaryThick subaerial volcanic sequences of probable mid Triassic age rest unconformably on Permo-Carboniferous limestones in the ‘Phyllite Series’ within the Gavrovo-Tripolitsa zone of the external Hellenide nappes. The volcanic rocks are varied in character. Pyroclastic rocks (often reddened) predominate, but minor basalt or andesite and rhyolitic hypabyssal intrusions and flows are also found. The rocks have experienced low-grade metamorphism and the only relict primary minerals are pyroxene and rare plagioclase in basic rocks and potash feldspar in acid rocks. The most important metamorphic phases are albite, chlorite, potassium mica, epidote, hematite, quartz and pumpellyite. Twenty-seven whole-rock major-element analyses suggest that there has been some exchange of Na2O and K2O for CaO during metamorphism, but that other elements have been relatively stable. A genetic interpretation of the rocks is attempted using published geochemical discriminator diagrams. The basic rocks are tholeiitic in major element chemistry and pyroxene composition. Trace element (Hf, Ta, Th, Ce, Yb) distribution suggests magma generation at a destructive plate margin.

Mineral Reactions in Shale Diagenesis: ABSTRACT

Compaction and lithification of muds (composed of normal terrestrial weathering minerals) into shales involves a major mineralogic change that has been followed in many sedimentary basins throughout the world. Unstable mineral components, such as potassium feldspar and mica, begin to decompose at temperatures around 60°C and the released chemical components react with dioctahedral smectite to produce mixed-layer illite/smectite, chlorite, and quartz. The extent of the reaction is highly dependent on temperature and time. This diagenetic reaction may influence the rate at which liquid hydrocarbons are generated because the surface electrical charge of smectite--and therefore its efficiency as a catalyst--increases during the reaction. In addition, dehydration of smectite on its conversion to illite can lead to overpressuring of pore fluids that may be involved in migration of liquid hydrocarbons from the shale to reservoir rocks. The timing of liquid hydrocarbon and new pore-water generation, and overpressuring caused by smectite dehydration may be critical to the production potential of a sedimentary basin. End_of_Article - Last_Page 939------------

Spectra of altered rocks in the visible and near infrared

Visible and near-infrared (0.35 to 2.5 mu m) bidirectional reflection spectra were recorded for a suite of well-characterized hydrothermally altered rock samples. The spectra typically display well-defined bands caused by both electronic and vibrational processes in the individual mineral constituents.Electronic transitions in the iron-bearing constituent minerals produce diagnostic minima near 0.43, 0.65, 0.85, and 0.93 mu m. Vibrational transitions in clay and water-bearing mineral constituents typically produce characteristic single or multiple features over limited spectral ranges near 1.4, 1.75, 1.9, 2.2, and 2.35 mu m. The most abundant feature-producing minerals present in these rocks are hematite, goethite, and alunite, while others frequently present are jarosite, kaolinite, potassium micas, pyrophyllite, montmorillonite, diaspore, and gypsum.This study shows that visible-near infrared spectrometry is a reliable and rapid technique for detecting and identifying clay minerals and alunite in rocks. Because these minerals are important constituents of altered rocks, the feasibility of using the visible and near infrared for detecting altered rocks by remote-sensing techniques is indicated. The spectral region near 2.2 mu m is particularly important for this purpose.

雲母粘土鉱物のX線底面反射パターン,特に含NH<SUB>4</SUB>雲母鉱物の特徴について

X-ray basal reflections of ammonium-bearing mica clay minerals found in the Tobe pottery stones of Ehime Prefecture have been examined in comparison with those of usual potassium mica clay minerals. Both the two mica clay minerals comprise mica and mica/montmorillonite interstratified minerals. The minerals with ammonium are characterized by larger basal reflection spacings and stronger first basal reflections than those of potassium mica minerals, which can be attributed to the interlayering of ammonium ions in place of potassium ions. The differences in basal reflections between the two mica clay minerals are well represented in I (10 Å)-I (5 Å)-I (3.3 Å) and W1-W2 (peak widths of about 10 Å and 5 Å reflections) diagrams.

Natural occurrence of a (Fe, Mn, Mg) tetrasilicic potassium mica

A mica whose structural formula: (K1.76Na0.31)(Fe2.22Mn1.29Mg0.99Ti0.28Al0.24□0.98) ·(Si7.33Al0.67)O20.26(F2.16OH1.58) closely approximates that of tetrasilicic potassium mica K2(M52+□)Si8O20(OH,F)4 where M2+ represents Mg2+, Fe2+, Mn2+, ..., has been discovered in the matrix of a peralkaline rhyolite (comendite) of the Mont-Dore massif (France). These micas had been obtained previously by synthesis only. In the groundmass of the rock, the micaceous phase is accompanied by a manganoan arfvedsonite, pyrophanite, magnetite, apatite, sphene, zircon and fluorite. The crystallographic properties of the mica are typically that of a tetrasilicic mica, with d060 = 1.533A and space group C2/m. There is a regular decrease of d060 (parameter b) with the ionic radius of the octahedral cation in synthetic micas containing Fe2+, Co2+, Mg2+, Ni2+. The purely Mn2+ end-member could not be synthesised; its instability is discussed on the basis of structural considerations. The conditions of crystallization of the micaceous phase are estimated to be 760 ° C, 800 bars with a fo2=10−14.7 bar. This mica has crystallized from a residual liquid, with high activity of silica and low activity of alumina, whose origin is discussed. The name MONT-DORITE is proposed for this natural tetrasilicic mica having Fe/Fe+Mg >1/2 and Fe/Fe+Mn >1/2. This name is from the stratovolcano Mont-Dore.

A test for excess radiogenic argon in micas

Radiogenic argon in excess of that produced by the in situ decay of potassium was first reported by Aldrich and Nier [1948] for the mineral beryl. Damon and Kulp [1958] reported a similar phenomenon for tourmaline and cordierite, as well as for beryl. Since then, excess argon has also been found in pyroxene [Hart and Dodd, 1962; McDougall and Green, 1964; Lovering and Richards, 1964] and in quartz and fluorite [Lippolt and Gentner, 1963; Rama et al., 1965]. The presence of excess argon has never been proved in the potassium micas which are so commonly used for K-Ar age determination.

Chemistry of soil minerals. Part III. Synthetic micas with substitutions of NH4 for K, Ga for Al, and Ge for Si

An investigation has been made of the hydrothermal synthesis of ammonium and potassium micas. The resultant ammonium aluminosilicate, gallosilicate, and gallogermanate micas have been compared with each other and with similarly prepared potassium aluminosilicate, gallosilicate, gallogermanate, and aluminogermanate micas. These micas have been characterised by their infrared spectra, by differential thermal and thermogravimetric analysis, and by X-ray diffraction. Unit cell dimensions and polytype character have been determined, and in the case of the potassium micas phases of compositions intermediate between those of the end-members have been prepared, and the relations between the dimensions of the unit cell and composition obtained.

The dielectric properties of mica

Two methods used for determining the dielectric constant of thin sheets of mica are described and the errors discussed. The results of measurements on over 170 sheets of mica are given. The samples tested included best clear mica, ruby, green and brown in colour, stained and spotted samples, and also samples with gaseous inclusions. There were also samples of amber mica and silver amber mica. The results show that practically all samples of muscovite (potassium mica) have the same dielectric constant, the most probable value being 7.0. The presence of inclusions has no great effect on this value. The samples of phlogopite (magnesium mica) - i.e., the amber micas - have rather lower dielectric constants, about 6.0 for normal amber mica, and 5.0 for the silver amber variety. Values of power factor are given for many of the samples. For the clear micas (muscovite) it may be as low as 0.0003, and possibly less. The effect of inclusions is to increase it considerably. The power factor of the amber micas is greater than that of the muscovite variety - about 0.02 for the clear amber and 0.05 for the silver amber variety. The samples were all about 8 cm. square and 0.1 mm. thick, and the measurements were all made on the Carey Foster bridge at a frequency of 800 cycles per second.