Granulite-facies metabasite ejecta in the Laacher See area,Eifel, West Germany

Near the village of Engeln, Laacher See area, garnet-bearing pyriclasite and pyribolite ejecta were recognized as constituents of alkaline basaltic tuffs; they are interpreted as fragments of the lowermost crust. During the first main stage of granulite facies metamorphism, assemblages with garnet (Alm₄₇Pyr₃₄Spess₂Gross + Andr₁₇), clinopyroxene (Wo₃₇En₃₅Fs₁₅Ts_8.5Jd_4.5), orthopyroxene I (En₃₄Fs₃₈Ts₄Jd₂), and plagioclase I (An₄₀-An₆₀) were formed in a temperature range of 730–850°C and rock pressures somewhere between 6.5 and 12 kb, $\text{P}{}_{\mathrm{tot}}\text{>}\text{P}{}_{\mathrm{<mtext>H</mtext>}}{}_2\text{O}\text{> 0}$. The rare sulfate-rich meionite, and at least a part of the ubiquitous brown hornblende were presumably also formed during this stage. A retrograde metamorphic event under slightly lower pressures and temperatures led to the breakdown of the assemblage garnet + clinopyroxene thereby forming coronas of plagioclase II $\text{(}\text{An}{}_{75}\text{) +}\text{orthopyroxene}\text{II +}\text{Ti-magnetite}\text{±}\text{brown hornblende}$.     

Petrogenesis of the Zoned Laacher See Tephra

The late Quaternary Laacher See phonolitic tephra deposit (EastEifel, W. Germany) is mineral-ogically and chemically zonedfrom highly evolved, volatile-rich and crystal-poor at its basetowards a mafic, crystal-rich phonolite at the top (Wörner& Schmincke, 1984). This zonation is interpreted as theresult of a continuous eruption from a zoned magma column. Majorand trace element evidence shows that the last erupted maficULST (Upper Laacher See Tephra) phonolite can be derived froma basanite parent magma via fractional crystallization of 30per cent clinopyroxene, 24 per cent amphibole, 4 per cent phlogopite,3.8 per cent magnetite, 2.5–3.0 per cent olivine and 1per cent apatite, leaving a derivative of 30 per cent evolvedmagma. Starting from the mafic (ULST) phonolite as a parent, the zonedsequence is postulated to have been formed by progressive fractionalcrystallization of the observed phenocryst phases. This modelwas tested by a series of 7 step-by-step mass balance fractionationcalculations. Abundance, modal composition and relative variationsof calculated fractionated phases agree well with the observedphenocryst abundances: sanidine followed by plagioclase andminor amounts of mafic phases are to be fractionated to givethe observed zoned sequence. The most evolved phonolite, however, cannot be generated bysubtraction of phenocrysts from the underlying phonolite. Processessuch as liquid-state differentiation may therefore have chemicallymodified the upper part (cupola) of the Laacher See magma columnsubsequent to crystal fractionation. The erupted phonolite magma (5.3 km³) was calculated to havestarted with a volume of 56 km³ of parental basanite magma whichfractionated to form 16.6 km³ of mafic phonolite. This magmafurther differentiated to give a 5.3 km³ zoned (erupted) phonolitecolumn. The non-erupted volume of 50 km³ is postulated to forma cooling cumulate body below the present day Laacher See volcano. The Laacher See magma system represents a complex end-membertype of a highly evolved small volume composition ally zonedmagma chamber with steep major and trace element gradients,the uppermost volatile rich magma layer resembling the stableroof part of rhyolitic chambers.     

The occurrence of Laacher See Tephra in Pomerania, NW Poland

A millimetre-thick bed of highly vesiculated pumiceous clasts was found in two peat bogs in Pomerania (NW Poland). Their phonolitic composition confirms the correlation with the Laacher See Tephra (LST). Based on the various CaO-Na₂O-K₂O content, most of these clasts can be linked with the Lower Laacher See Tephra (LLST), and some with the Middle Laacher See Tephra B (MLST-B). ¹⁴C dates obtained on peat samples are in agreement with an Allered stratigraphic position of that tephra. In several localities in NW Poland, it was found that there was no occurrence of tephra in peat bogs. Thus the presence of the LST is restricted to the northwestern fringes of Pomerania.     

Stable isotope relations in an open magma system,Laacher See,Eifel (FRG)

¹⁸O/¹⁶O and D/H ratios have been measured for matrix glasses and phenocrysts from the zoned phonolitic Laacher See tephra sequence (11000 y.b.p., East Eifel volcanic field, FRG) to study open-system behaviour of the associated magma system. Mineral and glass ¹⁸O values appear to be largely undisturbed by low-temperature, secondary alteration, record isotopic equilibrium and confirm previous conclusions, based on radiogenic isotope evidence, of early, small-scale crustal assimilation during differentiation of parental magmas in a crustal magma chamber. One sanidine-glass pair possibly documents the late stage influx of meteoric fluids into the topmost magma layer prior to eruption. A sealing carapace of chilled magma, which itself was strongly contaminated, prevented large-scale fluid exchange up to the point prior to eruption when this carapace was fractured and meteoric water gained access to parts of the magma system. D/H measurements of various glass types (glass inclusions, dense and pumiceous glass) and amphiboles gave conflicting results suggesting a combination of degassing, volatile exchange with country rocks and hydration. Stable isotope ratios for primitive parental magmas ( ¹⁸O=+5.5 to 7.0) and mantle megacrysts ( ¹⁸O=+ 5.5 to +6.0, D=–21 to –38, for amphiboles and phlogopite, resp.) suggest a rather variable fluid composition for the sub-Eifel mantle.     

The impact of the Laacher See Tephra on terrestrial and aquatic ecosystems in the Black Forest,southern germany

Late-glacial lake sediments containing the Laacher See Tephra (LST, 11000 yr BP) have been analysed for pollen and diatoms at two sites (Hirschenmoor, Rotmeer) in the montane belt of the Black Forest (southern Germany) in order to detect the possible impact of this major volcanic eruption on terrestrial and aquatic biota. The pollen assemblages at both sites show a minor increase in grasses and sedges following the tephra deposition, whereas the pollen of aquatic macrophytes do not show any consistent pattern. Partial redundancy analysis and Monte Carlo permutation tests suggest, however, that the LST had no statistically significant effect either on the terrestrial or aquatic pollen assemblages at either site when the effects of time and climatic change are allowed for statistically. The diatom assemblages at both sites changed after the deposition of the LST and diatominferred pH estimates suggest a short but non-significant excursion towards lower values. Multivariate analyses of the diatom data indicate a statistically significant impact of the deposition of the LST and associated changes in sediment lithology on the diatom assemblages when the effects of climatic change and time are allowed for statistically. However, owing to the interaction between tephra and lithology it is not possible to conclude if the diatom changes were caused by the deposition of the LST or by lithological changes.     

Impact of the Late Glacial Eruption of the Laacher See Volcano, Central Rhineland, Germany

Within a period of a few weeks toward the end of the Allerød Interstadial, the major Plinian eruption of the Laacher See volcano produced some 20 km³ of eruptiva, covering and preserving the late-glacial landscape in the German Central Rhineland over an area of more than 1000 km². Correlation of terrestrial archives with the Greenland ice-core records and improved calibration of the radiocarbon timescale permit a precise, accurate age determination of the Laacher See event some 200 yr before the onset of the Younger Dryas cold episode. Carbonized trees and botanical macrofossils preserved by Laacher See Tephra permit detailed regional paleoenvironmental reconstruction and show that open woodland were typical for the cool and humid hemiboreal climatic conditions during the late Allerød. This woodland provided the habitat for a large variety of animal species, documented at both paleontological and Final Paleolithic archeological sites preserved below Laacher See deposits. Of special interest are numerous animal tracks intercalated in Middle Laacher See deposits at the south of the Neuwied Basin. This knowledge may help to evaluate possible supraregional impacts of this volcanic event on northern hemispheric environment and climate during the late Allerød.     

Trace element abundances and mineral/melt distribution coefficients in phonolites from the Laacher See volcano (Germany)

Twenty six whole rocks, seven matrix and fifty three mineral separates from the compositionally zoned late Quaternary Laacher See tephra sequence (East Eifel, W Germany) were analyzed by instrumental neutron activation. These data document the chemical variation within the Laacher See magma chamber prior to eruption with a highly fractionated phonolite at the top and a more mafic phonolite at its base as derived from other data. Incompatible elements such as Zn, Zr, Nb, Hf, U, light and heavy rare earths are extremely enriched towards the top whereas compatible elements (e.g. Sr, Sc, Co, Eu) are strongly depleted. Semicompatible elements (Ta and some middle REE) are depleted at intermediate levels. This chemical variation is shown by whole rock and matrix data indicating the phonolite liquid was compositionally zoned regardless of phenocryst content. Hybrid rocks (phonolite-basanite) show the largest concentrations for compatible elements. All elements (except Rb) display continuous compositional variations with regard to the stratigraphic position of pumice samples. From these data we are able to distinguish three main units: An early erupted highly fractionated magma, the main volume of evolved phonolite and a mafic phonolite as the final products. The extreme variation of trace element distribution coef ficients (K) for 9 mineral phases with respect to stratigraphic position (resp. matrix composition) cannot be explained by conventional mechanisms. We postulate a significant modification of the trace element content of the phonolite melt by liquid-liquid controlled differentiation processes subsequent to and/or contemporaneous with (fractional) crystallization which caused disequilibrium between phenocrysts and host matrix. Therefore, our “distribution coefficients” deviate from equilibrium partition coefficients equivalent to the amount of this post crystallization modification of the matrix composition. The relationship between varying K and matrix composition is demonstrated by a ΔK-ΔM-diagram (variation of K versus variation of matrix, M). Different parts of this diagram relate to different parameters (T, P, polymerization, complex-building, equilibrium crystallization in a zoned magma column and post crystallization disequilibrium effects) which are responsible for the variation of distribution coefficients in general. The ΔK-ΔM-diagram may allow to distinguish between different processes affecting the distribution coefficients measured in natural volcanic rocks from a differentiating magma system.     

Antidune and chute and pool structures in the base surge deposits of the Laacher See area, Germany

Grey tuffs of late Pleistocene age form broad fans radiating from the Laacher See basin. They were derived from phreatomagmatic outbursts, and transported in turbulent pyroclastic flows, in contrast with the underlying white pumice tuffs of air fall origin. Flow origin of the grey tuffs is inferred from the well-bedded plane parallel to cross-bedded tephra characteristic of base surge deposits, and a variety of other sedimentary structures, as well as grain size distributions. We recognize a tentative sequence of five main kinds of dune structures or cross-bedded strata. With some reservations these may be compared with the high flow-regime alluvial bedforms produced experimentally in flumes. Most of the cross-bedded structures in the Laacher See deposits resemble antidunes, with steep stoss sides and very low-dipping lee sides. Upcurrent migration of antidune crests is dominant close to the source, but changes to downcurrent migration at greater distances, presumably because of decay in flow energy. The most spectacular cross-bedding is somewhat similar to chute and pool structures formed under experimental condition in alluvial flumes, but not recognized in ancient sedimentary rocks. We suggest that these structures of the Laacher See tuffs formed during deposition from phreatic pyroclastic flows of very high flow energy and high sediment concentration. The antidunes apparently formed at lesser flow velocity than chute and pool structures, although interpretation of velocity conditions by examination of the deposits is difficult because of other factors such as the cohesiveness of wet material erupted by explosive phreatic volcanic activity. The large wave lengths of the dune-like structures, however, suggest unusually high velocities. The Laacher See magmas were of phonolitic to tephritic composition, and may have erupted with greater explosive energy and in greater volume than comparable basaltic eruptions.     

Melting and Thermal Reconstitution of Pelitic Xenoliths, Wehr Volcano, East Eifel, West Germany

Pelitic xenoliths derived from amphibolite grade basement rocksoccur within a Pleistocene, trachytic, pyroclastic unit of theWehr volcano, East Eifel, West Germany: With increasing temperatureand/or prolonged heating at high temperature, quartz-plagioclaseand micaceous layers of the xenoliths have undergone meltingto form buchites and thermal reconstitution by dehydration reactions,melting and crystallization to form restites respectively. Thexenoliths provide detailed evidence of melting, high temperaturedecomposition of minerals, nucleation and growth of new phasesand P-T-f_o2 conditions of contact metamorphism of basement rocksby the Wehr magma. Melting begins at quartz-oligoclase (An_17·3Ab_82·3Or_0·4-An_20·0Ab_78·1Or_1·9)grain boundaries in quartz-plagioclase rich layers and the amountof melting is controlled by H₂O and alkalis released duringdehydroxylation/oxidation of associated micas. Initially, glasscompositions are heterogeneous, but with increasing degreesof melting they become more homogeneous and are similar to S-typegranitic minimum melts with SiO₂ between 71 and 77 wt. per cent;A/(CNK) ratios of 1·2–1·4; Na₂O < 2·95and normative corundum contents of 1·9–4·0per cent. Near micas plagioclase melts by preferential dissolutionof the NaAlSi₃O₈ component accompanied by a simultaneous increasein CaAl²Si²O⁸ (up to 20 mol. per cent An higher than the bulkplagioclase composition) at the melting edge. With increasingtemperature the end product of fractional melting is the formationand persistence of refractory bytownite (An_78–80) in thosexenoliths where extensive melting has taken place. Initial stage decomposition of muscovite involves dehydroxylation(H₂O and alkali loss). At higher temperatures muscovite breaksdown to mullite, sillimanite, corundum, sanidine and a peraluminousmelt. Mullite (40–43 mol. per cent SiO₂) and sillimanite(49 mol. per cent SiO₂) are Fe₂O₃ and TiO₂ rich (up to 6·1–0·84and 3·6–0·24 wt. per cent respectively).Al-rich mullite (up to 77 wt. per cent Al₂O₃) occurs with corundumwhich has high Fe₂O₃ and TiO₂ (up to 6·9 and 2·1wt. per cent respectively). Annealing at high temperatures andreducing conditions results in the exsolution of mullite fromsillimanite and ilmenite from corundum. Glass resulting fromthe melting of muscovite in the presence of quartz is peraluminous(A/(CNK) = 1·3) with SiO² contents of 66–69 percent and normative corundum of 4 per cent. Sanidine (An_1·9Ab_26·0Or_72·1-An_1·3Ab_15·9Or_82·9)crystallized from the melt. Dehydroxylation and oxidation of biotite results in a decreaseof K₂O from 8·6 to less than 1 wt. per cent and oxidetotals (less H₂O + contents) from 96·5 to 88·6,exsolution of Al-magnetite, and a decrease in the Fe/(Fe + Mg)ratio from 0·41 to 0·17. Partial melting of biotitein the presence of quartz/plagioclase to pleonaste, Al-Ti magnetite,sanidine(An_2·0Ab_34·9Or63·1) and melt takesplace at higher temperatures. Glass in the vicinity of meltedbiotite is pale brown and highly peraluminous (A/CNK = 2·1)with up to 6 wt. per cent MgO+FeO_{(total iroq)} and up to 10 percent normative corundum. Near liquidus biotite with higher Al₂O₃and TiO₂ than partially melted biotite crystallized from themelt. Ti-rich biotites (up to 6 wt. per cent TiO₂) occur withinthe restite layers of thermally reconstituted xenoliths. Meltingof Ti-rich biotite and sillimanite in contact with the siliceousmelt of the buchite parts of xenoliths resulted in the formationof cordierite (100 Mg/(Mg+Fe+Mn) = 76·5–69·4),Al-Ti magnetite and sanidine, and development of cordierite/quartzintergrowths into the buchite melt. Growth of sanidine enclosedrelic Ca-plagioclase to form patchy intergrowths in the restitelayers. Cordierite (100 Mg/(Mg+Fe+Mn) = 64–69), quartz,sillimanite, mullite, magnetite and ilmenite, crystallized fromthe peraluminous buchite melt. Green-brown spinels of the pleonaste-magnetite series have awide compositional variation of (mol. per cent) FeAl₂O₄—66·6–45·0;MgAl₂O₄—53·0–18·7; Fe₃O₄—6·9–28·1;MnAl₂O₄—1·2–1·5; Fe₂TiO₄—0·6–6·2.Rims are generally enriched in the Fe₃O₄ component as a resultof oxidation. Compositions of ilmenite and magnetite (single,homogeneous and composite grains) are highly variable and resultfrom varying degrees of high temperature oxidation that is associatedwith dehydroxylation of micas and melting. Oxidation mainlyresults in increasing Fe³⁺, Al and decreasing Ti⁴⁺, Fe²⁺ inilmenite, and increasing Fe²⁺, Ti⁴⁺ and decreasing Fe³⁺ in associatedmagnetite. A higher degree of oxidation is reached with exsolutionof rutile from ilmenite and formation of titanhematite and withexsolution of pleonaste from magnetite. Ti-Al rich magnetite(5·1–7·5 and 8·5–13·5wt. per cent respectively) and ilmenite crystallized from meltsin buchitic parts of the xenoliths. Chemical and mineralogic evidence indicates that even with extensivemelting the primary compositions of individual layers in thexenoliths remained unmodified. Apparently the xenoliths didnot remain long enough at high temperatures for desilicationand enrichment in Al₂O₃, TiO₂, FeO, Fe₂O₃, and MgO that resultsby removal of a ‘granitic’ melt, and/or by interactionwith the magma, to occur. T °C-f_o2 values calculated from unoxidized magnetite/ilmenitegive temperatures ranging from 615–710°C for contactmetamorphism and the beginning of melting, and between 873 and1054°C for the crystallization of oxides and mullite/sillimanitefrom high temperature peraluminous melts. f_o2 values of metamorphismand melting were between the Ni-NiO and Fe₂O₃-Fe₃O₄ buffer curves.The relative abundance of xenolith types, geophysical evidenceand contact metamorphic mineralogy indicates that the xenolithswere derived from depths corresponding to between 2–3kb P_load = P_fluid. The xenoliths were erupted during the latestphreatomagmatic eruption from the Wehr volcano which resultedin vesiculation of melts in partially molten xenoliths causingfragmentation and disorientation of solid restite layers.     

Zoning and exsolution in alkali feldspars from Laacher See volcano (Western Germany): constraints on temperature history prior to eruption

Compositional zoning and exsolution patterns of alkali feldspars in carbonatite-bearing cognate syenites from the 6.3 km³ (D.R.E) phonolitic Laacher See Tephra (LST) deposit in western Germany (12.9 ka) are reported. These rocks represent the cooler outer portion and crystal-rich products of a cooling magma reservoir at upper crustal levels. Major and trace-element difference between cores and rims in sanidine crystals represent two generations of crystal growth separated by unmixing of a carbonate melt. Trace-element differences measured by LA–ICP–MS are in accordance with silicate–carbonate unmixing. Across the core–rim boundary, we extracted gray-scale profiles from multiple accumulations of back-scattered electron images. Gray scales directly represent K/Na ratios owing to low concentrations of Ba and Sr (<?30 ppm). Diffusion gradients are modeled to solve for temperature using known pre-eruptive U–Th zircon ages (0–20 ky) of each sample (Schmitt et al., J Petrol 51:1053–1085, 2010). Estimated temperatures range from 630 °C to 670 °C. For the exsolution boundaries, a diffusive homogenization model is constrained by the solvus temperature of ~ 712^_725 °C and gives short time scales of only 15–50 days. Based on our results, we present a model for the temperature–time history of these rocks. The model also constrains the thermal variation across the cooling crystal-rich carapace of the magma reservoir over 20 ka and suggests a thermal reactivation of cumulates, the cooling carapace, and probably the entire system only a few years prior to the explosive eruption of the remaining molten core of the phonolitic magma reservoir.     

Lithofacies succession of maar crater deposits in the Eifel area (Germany)

ABSTRACT Maar craters often contain exceptionally preserved fossils and maar sediments may reflect detailed environmental changes. Volcanosedimentary processes in a Middle Eocene maar crater lake are illustrated by the deposits of Eckfeld Maar in the Tertiary Hocheifel Volcanic Field (Rhenish Massif, Germany). The maar origin of the basin is evident from a circular negative gravity anomaly which indicates a low-density funnel-shaped basin filling. From the facies analysis of an Eocene (Eckfeld) and a Pleistocene (Döttingen) maar we develop a lithozone classification for the interpretation of maar sediments: syn-/post-eruptive breccias are followed by a fining-upwards sequence of lacustrine mud with coarse layers and final swamp deposits. From the facies analysis and regional geological data we reconstruct the pre- to post-eruptive history of a maar crater prior to post-Eocene uplift. These observations can be used for the interpretation of Tertiary and Quaternary maar craters that are ideal fossil and sediment traps.     

Carbonatite in the tuffs of the West Eifel,Germany

Newly-discovered carbonatitic fragments from the West Eifel are described in terms of their petrography and trace-element content.     

Multiple Enrichment Processes and their Relationships in the Subcrustal Lithosphere Beneath the Eifel (Germany)

Three types of enrichment processes may be distinguished inspinel peridotite mantle xenoliths from the West Eifel (Germany):

1. Enrichmentof light rare earth elements (LREE) occurs in wholerocks andclinopyroxenes in conjunction with the formation ofTi-pooramphiboles (<0•5%) in a low-tempetature suite(900C).
2. Enrichment in high field strength elements (HFSE; Ti and Hf)is associated with strong zoning of TiO₂ in amphibole adjacentto mica hornblendite veins. A reheating from 900 to 1050C associatedwith this vein formation is reflected by the zoning profilesin orthopyroxenes with Ca, Al, and Cr increasing from core torim.
3. Moderate enrichment of LREE without amphibole formationin ahigh-temperature suite (1125C) is observed at the contactofperidotites to pyroxenite veins yielding the same temperature.
4. Based on geochemical and isotopic evidence, enrichment process(1) is inferred to be due to interaction of peridotites fromthe subcrustal lithosphere with low-density fluids. Process(2) represents a subsequent interaction of amphibole-bearingperidotites formed during the first process with basic meltsmoving through a system of cross-cutting dykes and veins. Processes(2) and (3) are linked to the Quaternary West Eifel volcanism.Geothermobarometry of the xenoliths shows that these processesare related to different depth regimes of the lower lithosphere.

     

Palynological analyses in the laminated sediment of Lake Holzmaar (Eifel, Germany): duration of Lateglacial and Preboreal biozones

The laminated sediment of Lake Holzmaar (Germany) has provided a continuous varve chronology for the last 3500 varve years (vy) and beyond that a floating varve chronology back to more than 22500 vy BP. This chronology in calendar years, in combination with palynology, enables us to determine the timing and the magnitude of Lateglacial and Early Holocene environmental changes on land (from 13838 to 10930 vy BP). The palynological diagram has a mean time resolution of 27 vy between samples. This paper establishes for the first time the biozonation for Lake Holzmaar below the Laacher See Tephra. Fifteen pollen subzones grouped in four biozones are defined by cluster analysis. After a period disturbed by microturbidites, only a part of the Bølling is present. Three cold periods have been evidenced by pollen analyses: the Older Dryas (96-vy-long), the Younger Dryas (654-vy-long) and the Rammelbeek phase (237-vy-long). The Allerød (883-vy-long) is bipartite with a first Betula -dominated period followed by a Pinus -dominated one. The Younger Dryas is also bipartite, with first a decrease of winter temperatures along with a change to a more continental climate. It is followed by a drier phase with a second decrease in temperatures, probably this time also affecting summer temperatures. The Preboreal is 702-yr-long. The duration of most phases corresponds to published records, except for that of the Younger Dryas. Cluster and rate-of-change analyses indicate a sharp change in the terrestrial vegetation assemblages that may be caused by a sedimentary hiatus of erosive origin during this cold and dry period. As a result, the chronology of Holzmaar has to be revised most likely below the middle of the Younger Dryas. Comparison with the varve record of Meerfelder Maar, a neighbour maar lake, suggests adding 320 vy below 12025 vy.     

The nature and geological history of the deep crust under the Eifel, Germany

The crust ≈ 10–20 km under the Eifel is composed of amphibolite-facies metasediments and meta-igneous rocks of tonalitic to granodioritic composition; mafic granulites occupy the base of the crust down to a Moho depth between about 29 and 34 km. The meta-granodiorites and meta-tonalites have I-type chemical characteristics and appear to have formed approximately 400 Myr ago by partial melting of a lower crustal source. Amphibolite-facies metamorphism probably followed within the same orogeny. During the Quaternary, many amphibolite-facies rocks were subjected to contact heating in crustal magma chambers and/or during transport to the earth's surface. Contact heating is also recorded in radiogenic isotope compositions of minerals from one xenolith. A genetic link between meta-igneous amphibolites and the deeper crustal mafic granulites can neither be proven nor discounted by the isotope data. If there is a genetic relationship, it requires fractionation of a mafic magma in the lower crust and assimilation of metasediments and separation of a highly evolved melt.     

First terrestrial occurrence of roedderite in volcanic ejecta of the Eifel,Germany

Idiomorphic crystals of roedderite occur in melt-coated cavities of xenoliths of contact-altered quartz-sillimanite and quartz-feldspar gneisses which were ejected with the tephritic lava of the Bellerberg volcano. Physical and chemical properties of three different sets of crystals agree generally with those of roedderites from meteorites, in which so far the mineral had been found exclusively. In detail, however, there are characteristic chemical differences amongst the Eifel roedderites with one set of crystals matching closely the ideal formula (Na,K)₂Mg₅ Si₁₂O₃₀, a second set containing excess alkalies according to the substitution Na⁺0.5 Mg²⁺, and a third set richer in iron having an alkali deficiency following Fe³⁺Fe²⁺+Na⁺.The terrestrial roedderites are considered to be precipitates from highly alkaline, MgSi-rich, but Aldeficient gas phases that evolved through contact heating of the gneisses by the tephrite magma.