000214   Krishnamurthy V;Shukla J (Center for Ocean-Land-Atmosphere Studies, Institute of Global Environment and Society, Inc. 4041 Powder Mill Road, Suite 302, Calverton, MD 20705) : Observed and model simulated interannual variability of the Indian monsoon. Mausam 2001, 52(1), 133-50.

Center for Ocean-Land-Atmosphere (COLA) general circulation model has been integrated seven times with observed global sea surface temperature (SST) for the years 1979-98. The model-simulated annual cycle, the seasonal mean and the interannual variability of the summer monsoon rainfall and circulation over the Indian region are compared with the corresponding observations. It is found that, although this model ahss shown remarkable success in simulating the local and global response of tropical SST anomalies, the model shows poor skill in simulating the interannual variability of monsoon rainfall over India. While it is true that the correlation between the observed tropical Pacific SST and the Indian summer monsoon rainfall for the most recent 20 years itself is considerably lower than that for other 20 years periods in the past, it is likely that the model's inability to stimulate rainfall variability over India is largely related to the systematic errors of the model in simulating the climatological mean monsoon circulation and rainfall, especially over the oceanic regions.

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000213   Karbassi A R;Shankar R;Manjunatha B R (NO, Institute of Environmental Studies, Tehran University, P.O. Box 14155-6135, Tehran) : Geochemistry of shelf sediments off Mulki on the southwestern coast of India and their palaeoenvironmental significance. J Geol Soc India 2001, 58(1), 37-44.

Geochemical and textural variations of these sediments suggest changes in the depositional environments: Sediments of the lower zone were deposited in a marshy environment when the core site was close to the shore during the late Pleistocene low stand of sea level. The late Quaternary sea level rise led to a shift in the depositional environment - from marsh to a still stand beach environment-when silty sands were deposited. Although the core site has been in the shelf since the beginning of Holocene, there has not been much sedimentation not only because of the negligible quantity of sediment supplied by the small west-flowing rivers but also due to the rapid rise in sea level during early Holocene. The reconstructed depositional history of the core is in consonance with the recently proposed sea level curve for the western continental margin of India.

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000212   Joshi P C;Simon B;Thapliyal P K (Atmospaheric Sciences Division, Space Applications Centre, , Ahmedabad-380 015) : Satellite estimated water vapour in relation to Asian monsoon circulation. Mausam 2001, 52(1), 109-16.

Water vapour plays a crucial role in various exchange and transport processes in the atmosphere and its knowledge in the tropics is extremely important for input to various global circulation models. The vast oceans of earth's surface provide a large source of moisture and continuously modify the thermodynamics of the atmosphere through latent heat flux and condensational heating. In the tropics, especially in the Indian ocean the water vapour is highly heterogeneous in nature, and is one of the parameters which is responsible for cloud formation, associated with tropical systems like monsoon flows, depression, cyclones etc. Reviews the various informations available from deferent geostationary and polar orbiting satellites about water vapour affecting the southwest monsoon region around the Indian Ocean and Indian subcontinent. The temperature and moisture data from TIROS operational vertical sounder (TOVS) and INSAT-2E water vapour channel are examined to study water vapour distribution. Their usefulness in characterizing the Asian south-west (SW) monsoon circulation is focused. The Western Indian ocean showed an increase in mid-tropospheric moisture (700-500 hPa) over about 8 to 10 days prior to the onset over Kerala coast. NOAA/TOVS layer temperature and humidity is used to extrapolate the humidity profile at standard pressure levels. It is also used to compute latent and sensible heat flux.

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000211   Joshi A (Dept. Earth Sci, Kurukshetra University, Kurukshetra-136 119) : Strong motion envelope modelling of the source of the Chamoli earthquake of March 28, 1999 in the Garhwal Himalaya, India. J Seismol 2001, 5(4), 499-518.

Chamoli earthquake of March 28, 1999 was recorded at 11 different stations of a strong motion array installed in the epicentral region. The maximum peak ground acceleration (353 cm/s(2)) was recorded at an accelerograph located at Gopeshwar. The data from eleven stations has been used for comparison with the simulated acceleration envelopes due to a model of the rupture responsible for this earthquake. For simulation of acceleration envelope the method of Midorikawa (1993) has been modified for its applicability to Himalayan region. This method has earlier been used by Joshi and Patel (1997) and Joshi (1999) for the study of Uttarkashi earthquake of 20th Oct, 1991. The same method has been used for study of Chamoli earthquake. Layered earth crust has been introduced in place of homogeneous one in this method. The model of rupture is placed at a depth of 12 km below the Munsiari thrust for modelling Chamoli earthquake. Peak ground acceleration was calculated from simulated acceleration envelope using layered as well as homogeneous earth crust. For the rupture placed in a layered crust model peak ground acceleration of order 312 cm/s(2) was simulated at Gopeshwar which is quite close to actually recorded value. The comparison of peak ground acceleration values in terms of root mean square error at eleven stations suggests that the root mean square error is reduced by inclusion of a layered earth crust in place of homogeneous earth crust.

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000210   Jassal H S;Gill G S;Sidhu P S (Department of Soils, Punjab Agricultural University, Ludhiana-141 004) : Clay mineralogy and major element geochemistry of the upper Siwalik sequence of Punjab, Northwestern Himalaya. J Geol Soc India 2001, 58(2), 113-22.

X-ray diffraction and major element analyses of the upper Siwalik rocks of Punjab were carried out to assess the clay mineral composition of the rocks. The clay mineral assemblages comprise illite, smectite, kaolinite, chlorite and mixed layer phyllosilicates. The SiO2/Al2O3 and SiO2/R2O3 molecular ratios of the clays range between 3.86 and 6.60, and 2.94 and 5.37 respectively, suggesting dominance of 2:1 type clay minerals in these rocks. Inheritence and transformation were recognized as the chief processes responsible for genesis of these clay minerals. The clay mineral assemblages suggest their formation under moderate chemical weathering conditions in cool to temperate climate.

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000209   Jain C K;Sharma M K (NO, Natl Inst Hydrol, Roorkee-247 667) : Distribution of trace metals in the Hindon River system, India. J Hydrol 2001, 253(1-4), 81-90.

Distribution of trace metals (Cu, Zn, Fe, Mn, Cd, Cr, Pb, and Ni) in water, suspended and bed sediments of the River Hindon, a highly polluted river in western Uttar Pradesh (India) has been studied. The river is polluted by municipal, industrial and agricultural effluents, and flows through the city of Saharanpur, Muzaffarnagar and Ghaziabad districts. The heavy metal concentrations in water were observed to depend largely on the Sediment analysis indicates that the large amount of heavy metals is associated with organic matter, the fine-grained sediment fraction and Fe/Mn hydrous oxides. A high positive correlation of most of the metal ions in sediments with iron, manganese and organic matter indicate that these constituents play a major role in transport of metal ions. The heavy metal concentrations generally increased with the decreasing particle size of the sediments. Lower metal concentrations in bed sediments during post-monsoon season established that monsoon had a slight effect on status of metals in sediments by causing renewal and mobilization of metals from the sediments.

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000208   Jagadheesha D;Ramesh R (Physical Research Laboratory, , Ahmedabad-380 009) : Past monsoons - a review of proxy data and modelling. Mausam 2001, 52(1), 275-84.

Recent modelling studies have given insight into the role of internal feedback processes among components of the climate system on the evolution of monsoon strength since the Last Glacial Maximum (21,000 years ago). Presents an overview of these modelling studies related to the summer monsoon over India and northern Africa. These studies indicate that the seasonal insolation changes alone do not explain the observed extent of hydrological changes during the early and middle Holocene over northern Africa. To simulate the extent of observed changes during this period incorporation of vegetation as an active component in climate models appears to be necessary. Over the Indian region, model results show that precipitation-soil moisture feedbacks play an important role in determining the response of the monsoon to changes in insolation and glacial-age surface boundary conditions. Indian monsoon strength from proxy records during the early and middle Holocene have also been used in conjunction with coupled ocean atmosphere general circulation model experiments to refute the suggestion that semi-permanent warm surface conditions prevailed over equatorial Pacific ocean from 11 to 5 ka.

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000207   Goswami B N;Manu Anna Thomas (Center for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore-560 012) : Decadal variations of hadley and walker circulations in the tropics. Mausam 2001, 52(1), 23-36.

Preliminary estimate of divergent Hadley and Walker circulation associated with inter-decadal variations in the tropics is made with 50-year reanalysis data and compared with their inter-annual counterparts. Interdecadal and inter-annual components are seperated using harmonic analysis and meridional and zonal mass flux stream functions are used to calculate the strength of Hadley and Walker circulations. The magnitude of inter-decadal Hadley and Walker circulation anomalies are shown to be comparable to those associated with dominant inter-annual variations. How superposition of inter-decadal and inter-annual divergent circulations may influence regional climate is discussed.

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000206   Gandhi M S;Seetharamaiah J;Bhanu Murty P (NO, Delta Studies Institute, Andhra University, Visakhapatnam-530 003) : An indigenous approach to low cost portable vibracoring in deltaic environments. J Geol Soc India 2001, 58(2), 176-8.

Simple but very effective and inexpensive indigenous method of vibracoring has been developed for acquisition of continuous cores in subaqueous environments at water depths of below 2m. The principal components are the following: 3.5 HP concrete vibrator, irrigation PVC tube, tripod and pulley. The entire system weighs 50 kg and approximately costs about Rs. 25,000/-. This system was operated successfully in the transitional sedimentary environments of the East Coast deltas by collecting around 100 cores averaging to 2 m in length. Sediments ranging from clay to coarse sand have been recovered using this system. Percentage of recovery was usually 60 to 100 and distortion of delicate sedimentary structures was generally minor.

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000205   Deo A A;Salvekar P S;Behera S K (NO, Indiana Institute of Tropical Meteorology, Pune-411 008) : Oceanic response to cyclone moving in different directions over Indian seas using IRG model. Mausam 2001, 52(1), 163-74.

IITM Reduced Gravity (IRG) ocean model is employed to investigate the influence of tropical cyclone moving in different directions in Indian Seas. Some of the observed storm tracks in the Arabian Sea and Bay of Bengal are considered which have northward and westward movement. Sensitivity study is carried out for initial position of the storm at (90°E, 10°N) and moving in different directions. For westward moving cyclones the right bias in the model upper-layer thickness deviation (ULTD) field disappears. In an another experiment of westward moving cyclone originating at different latitudes, the ocean response is found to be sensitive to the Coriolis parameter (↵). The surface currents as well as ULTD reduce, as ↵, increases. The amplitude and the wavelength of inertia gravity wave increase with decrease in <255>, in the wake of the cyclone. This study helps to determine the upwellig region arising due to movement of the cyclone.

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000204   Chandran P;Ray S K;Bhattacharyya T;Krishnan P;Pal D K (Division of Soil Resource Studies, National Bureau of Soil Survey and Land Use Planning, Amravati Road, Nagpur-440 010) : Clay minerals in two ferruginous soils of southern India. Clay Res 2000, 19(2), 77-85.

Two Benchmark ferruginous soils namely Jamkhandi and Palathurai have been taken for the study. In contrast to the general understanding, these ferruginous soils are calcareous and alkaline in nature. Layer silicates present in silt, coarse clay and fine clay fractions of these soils are also in sharp contrast to those of ferruginous soils reported earlier. Dominant presence of smectite in all the size fractions is very common alongwith mica. Kaolinite is present in Jamkhandi soils. Under the prevailing semi-arid environment neither such a huge amount of smectite nor kaolinite can be formed. These soils have suffered truncation as evident from their thin Ap horizon followed by Bt horizon of <62> 30 per cent clay, exposing a relatively unweathered soil formed in pre-Pliocene tropical humid climate. Smectite in fine clay fractions of Jamkhandi soils have both high and low charge density, whereas smectite in silt and coarse clay fractions have high charge. Mica present in silt and coarse clay fractions consists of more biotite than muscovite and it survived trpical weathering. In the present semi-arid climate biotite has weathered to high charge smectite. Aridity also induced the precipitation of calcium carbonate. High amount of weatherable minerals in ferruginous soils of southern India has distinct relevance in their water and K-management.

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000203   Casshyap S M;Bhardwaj B D;Raza M;Singh A;Khan A (Department of Geology, Aligarh Muslim University, Aligarh-202 002) : Barrier inlet and associated facies of shore zone: an example from Khardeola formation of lower vindhyan sequence in Chittaurgarh, Rajasthan. J Geol Soc India 2001, 58(2), 97-11.

Deposits are interpreted as originating within laterally migrating tidal inlets (barrier inlets), in which easterly oriented ebb currents were dominant, with intermittent influx of flood oriented and north or south directed longshore currents. Plane bedded to gently inclined units of quartzarenite are interpreted as beach foreshore (spit) deposits that occur in places, capping the barrier inlet sequence. A combination of barrier inlet migration and shoreline transgression resulted in a truncated and modified barrier island sequence, dominated by inlet fill sandstone that merges with or oversteps westward (landward) the interlayered, fine grained clastic lagoonal/tidal flat facies. The Khardeola sedimentation was terminated with the decline in sediment supply, rise in sea level and landward migration of shoreline, followed by deposition of the overlying algae dominated Bhagwanpura Limestone in a quiet, open shelf of transgressive phase.

000202   Borgaonkar H P;Pant G B (NO, Indian Institute of Tropical Meteorology, Pune-411 008) : Long-term climate variability over monsoon Asia as revealed by some proxy sources. Mausam 2001, 52(1), 9-22.

Studies on climate variability over the region of monsoon Asia mostly during the Quaternary. Based on various sources of proxy data have been reviewed. Increasing interest to understand the processes of monsoon system over the Asian region as well as the availability of data from variety of reliable proxy sources such as, ocean sediments, ice cores and historical documents have encouraged the palaeoclimatic studies in this region. Inferences drawn from the multiproxy sources indicate good association of glacial and inter-glacial phases with over all monsoon flow. Warm and wet periods are generally characterized by strong summer monsoon, where as, weak monsoonal activities were observed during cold and dry periods. All India monsoon rainfall since early 17th century based on dendroclimatic reconstructions shows trend-less nature with large interannual variability as seen in the instrumental record of recent century. Historical evidences over this region are a potential source of information on contemporary climate change.

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000201   Bisht B S;Rajasekaran P;Sinha R M (Atomic Minerals Directorate for Exploration and Research, Department o, , Begumpet, Hyderabad-500 016) : Fluid inclusion characteristics of unconformity-related uranium mineralisation, Lambapur-Peddagattu area, Andhra Pradesh. J Geol Soc India 2001, 58(1), 45-51.

Aqueous bi-phase fluid inclusions in quartz from mineralised vein, granite and pebbly quartzite have been studied to decipher physico-chemical conditions of the unconformity-related uranium mineralisation at Lambapur-Peddagattu area in the northern fringe of Cuddapah basin. Fluid inclusions in vein- and granitic- quartz show significant similarity in phase ratios and homogenisation temperatures, though they differ in the mode of origin. The main population of inclusions in vein quartz is of primary origin, while in granitic quartz it is of secondary origin. The size of fluid inclusions generally varies between 10μm to 20μm, with low gas to liquid ratios corresponding to high degree of fill (F=0.8 to 0.9). Inclusions in vein- and granitic- quartz homogenise to liquid phase between 140°C to 240°C (mode 150°C to 170°C) [TH]. Similar temperature of homogenisation has been obtained in quartz of pebbly quartzite. The ice melting temperatures in vein quartz are in the range of -2°C to 10°C [TM] equivalent to salinity of 1-14 wt% eNaCl and in granitic quartz these are in the range of -6°C to - 14°C [TM] corresponding to salinity values of 10-18 wt ° eNaCl.

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000200   Bhattacharyya T;Srivastava P;Pal D K (Division of Soil Resource Studies, National Bureau of Soil Survey and Land Use Planning, Amravati Road, Nagpur-440 010) : In search of parental legacy for Gibbsite in soils. Clay Res 2000, 19(2), 69-75.

Proportions of kaolin and gibbsite are often inversely related in the soil profile and sum of these two minerals within the solum maintains a constancy which may suggest the formation of gibbsite at the expense of kaolin. Although the summation of clay K1/HIC and gibbsite in two representative Ultisols of north-east India show an apparent constancy, the transformation of kaolin to gibbsite is not feasible since kaolin is still in an intermediate stage as K1/HIV, which is yet to be fully transformed to kaolin. Such contrasting quantitative depth distribution of minerals is often observed even though there is no parental legacy between these minerals. The presence of both HIV and gibbsite in Ultisols indicates that the anti-gibbsites it is concluded that the formation of gibbsites at the expense of primary mineral in these Ultisols carries a signature of earlier alkaline pedochemical weathering. The occurrence of gibbsites should not therefore be considered as a conclusive evidence of advanced weathering conditions of soils.

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000199   Bhaskar Rao D V;Naidu C V;Srinivasa Rao B R (Department of Meteorology and Oceanography, Andhra University, Visakhapatnam) : Trends and fluctuations of the cyclonic systems overnorth Indian ocean. Mausam 2001, 52(1), 37-46.

Data of the monthly cyclone frequencies over North Indian Ocean for the period 1877-1998 has been analysed to study the long-term trends and fluctuations. Analysis has been made separately for depressions and cyclones for the pre-monsoon, monsoon and post-monsoon seasons along with the annual frequencies. The data was subjected to 11-year moving averages and the epochs of increasing and decreasing trends have been identified. A consistent decreasing trend after 1950s is a notable feature. The time series of the monthly cyclone frequency were passed through a high-pass filter to eliminate periods greater than 21 years and then subjected to spectrum analysis using Maximum Entropy Method to obtain dominant periodicities. Three significant periodicities at 2.2-2.8; 3.5-6.5 and 10-15 years have been identified which could be attributed to QBO, ENSO and decadal frequencies.

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000198   Beig G (NO, Indian Institute of Tropical Meteorology, Pune-411 008) : Model evolution of the middle atmospheric palaeoenvironments. Mausam 2001, 52(1), 297-306.

Ice core air analysis has indicated a significant variation in the atmospheric contents of the greenhouse gases CO2, CH4 and N2O from the last ice age to the present period. This may have contributed in altering the vertical distribution of temperature and composition of the atmosphere about which not much information is available. The two dimensional interactive model of radiation, dynamics and chemistry has been used to reconstruct the annual vertical distribution of thermal structure and trace gas concentrations of the middle atmosphere for the periods extending from last ice age to the present. For this purpose, ice core air data of the above mentioned forcing parameters are used as input to the model for different time frames including Mounder Maximum, Roman maximum, pre- industrial period and the last glacial period. Model results show that the considerable reduction in the greenhouse gas content for the last ice age has resulted in cooling of troposphere and a warming by about 10 to 15° K in the upper stratosphere as compared to present. The variation in temperature is closely related with the water vapour content. The percentage change in ozone concentration for the last glacial period is to a maximum of 50% near the poles in the upper stratosphere and about 10% in the tropics.

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000197   Becker B D;Slingo J M;Ferranti L;Molteni F (Centre for Global Atmospheric Modelling, Department of Meteorolgy, University of Reading, Trieste, Italy) : Seasonal predictability of the Indian summer monsoon: what role do land surface conditions play. Mausam 2001, 52(1), 175-90.

Anomalous springtime snow amount over Eurasia may provide long term memory to the climate system by affecting the land surface energy and moisture budgets. In turn the anomalous land surface conditions introduced by snow anomalies may influence monsoon variability. Results from a programme of seasonal forecast ensembles are used to address, specifically, the influence of western Eurasian land surface conditions on the variability and hence predictability of the Indian summer monsoon. The factors that are important for establishing spring time land surface conditions over western Eurasia, particularly snow amounts are also investigated. The results have shown that high snow amounts over western Eurasia are linked to La Nina, suggesting that the El-Nino/Southern Oscillation (ENSO) has in influence on the wintertime climate of Eurasia. The signature of these snow depth anomalies is carried through to the summer in terms of changes in soil wetness and surface temperatures. An ensemble of summer integrations with climatological sea surface temperature (SST) has been used to investigate the impact of these anomalous land surface conditions on monsoon variability. The results have shown that the monsoon circulation in substantially weakened in association with above normal snow amounts over western Eurasia, whilst All India Rainfall is slightly increased.

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000196   Bajpai U;Madhav Kumar;Shukla M;Anand-Prakash; Srivastava G P (NO, Birbal Sahni Institute of Palaecobotany, 53, University Road, Lucknow-226 007) : Nature and composition of pyrite framboids and organic substrate from degraded leaf cuticles of late tertiary sediments, Mahuadanr valley, Palamu, Bihar. Curr Sci 2001, 81(1), 102-6.

Detailed studies of pyrite framboids from degraded leaf cuticles have been carried out under scanning electron microscopy (SEM) and energy-dispersive X-ray analyser system (EDAX). The investigations indicate that framboidal pyrites form in the cavities and cell lumen of degraded leaves and other plant entities under reducing conditions. They occur in clusters and as solitary spherules. The elemental analyses indicate that the carbon, nitrogen, oxygen, phosphorus, iron and sulphur are the main constituents of framboids developed on the organic substrate. The morphological characters of bacterial colonies are generally retained during mineral uptake to form framboids.

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000195   Bachiochi D;Jha B;Krishnamurti T N (NO, Florida State University, Department of Meteorology, Tallahassee FL 32306-452, USA) : Effect of Indian Ocean warming on the Indian monsoon: an atmospheric model study. Mausam 2001, 52(1), 151-62.

Results from an atmospheric modeling study using the Florida State University Global Spectral Model indicate that, in years such as 1997 when the Indian Ocean SSTs are large,, the Indian monsoon exhibits a typical behaviour. During that year, an extended shift of the tropical convergence zone towards the north played a role in the regional Hadley cell anomalies. The local warm boundary conditions in the northwestern Indian Ocean aided the high rainfall anomaly in Western India during the model simulations. The upper level structure, exhibited in terms of the global velocity potential is slightly shifted east for 1997, but with the correct sign,. This structure shows regions of convergence over Indonesia where severe drought had occurred. The performance of the model rainfall over the equatorial Indian Ocean was uncanny for most seasons studied. Overall, the model performed best over the oceanic regions.

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000194   Asnani G C (NO, Indian Institute of Tropical Meteorology, Pune-411 008) : El nino of 1997-1998 and Indian monsoon. Mausam 2001, 52(1), 57-66.

El-Nino of 1997-1998 was accompanied by severe global weather anomalies, which generated widespread interest at all levels in the world. As a result, united Nations General Assembly passed a resolution (52/200) urging International co-operation to reduce the adverse impact of El-Nino on human society and Environment. The El-Nino (Warm Phase) commenced around April - May 1997, reached peak intensity around December 1997 and ended around May 1998. La-Nina (Cold phase) started around this time, reached its peak in January 1999. Development and decay of the El-Nino are illustrated through SST, SOI and sea-water temperature below the sea-surface. Features during peak period of El-Nino are illustrated through SST, sea-level pressure, surface wind, OLR, and Walker Circulation. There is clear evidence of west-to-east propagation of OLR anomaly, 850 hPa zonal wind anomaly and sea-level pressure anomaly. SST anomaly pattern did not give strong evidence of this type of zonal progression. El-Nino is global in nature. El-Nino/La-Nina years during the 120-year period 1871 - 1990 are tabulated along with All India Summer Monsoon Rainfall (AISMR) amomalies. There is evidence of El-Nino years tending to become years of deficit rainfall and La-Nina years being years of excess rainfall over India. El-Nino/La-Nina events, which can be predicted 6-12 months in advance, can be used and are being used as part of the prediction formulae,

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000193   Anil Kumar;Gopalan K;Rao K R P;Nayak S S (NO, National Geophysical Research Institute, Uppal Road, Hyderabad-500 007) : Rb-Sr age of kimberlites and lamproites from eastern Dharwar craton, South India. J Geol Soc India 2001, 58(2), 135-41.

Acid-leached phlogopite Rb-Si isochron ages of the Kotakonda and Mudalbid kimberlites in the Narayanpet kimberlite field northwest of the Cuddapah basin, south India are 1085±14 and 1099±12 Ma, respectively. These concordant ages are much younger than the recently reported K-Ar and <^>40Ar-<^>39Ar ages of 1363±48 and 1402±5 Ma, respectively for the former kimberlite, and support out earlier conclusion that the south Indian kimberlites erupted episodically close to 1090 Ma ago. Three lamproites - one each from Ramannapeta at the northeastern margin and Chelima and Zangamarajupalle within the Cuddapah basin - give distinctly different Rb-Sr ages of 1224±14, 1354±17 and 1070±22 Ma, respectively. While the Rb-Sr age of the Ramannapeta lamproite is also younger than an earlier reported K-Ar age of 1381±18 Ma, it is the same as that of many spatially close alkaline complexes like at Elchuru and Kunavaram. The ages for the Chelima and Zangamarajupalle rocks are only tentative, as these rocks contain a large secondary carbonate component with its Sr isotopic composition genetically unrelated to that of their phlogopites.