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DISPUTED, FORGOTTEN, REVITALIZED: ALEMONITE - AN ENIGMATIC IMPACT BRECCIA
PROBABLY LINKED TO THE RIES CRATER (GERMANY) IMPACT EVENT. K. Ernstson1, M. Molnár2,
M. Hiltl3, K. Ventura4 1Faculty of Philosophy I, University of Würzburg, D-97074 Würzburg, Germany
(kernstson@ernstson.de) 2Resselovo nám. 76, Chrudim 537 01, Czech Republic (molnar@ego93.com) 3Carl Zeiss
Microscopy GmbH, D-73447 Oberkochen, (mhiltl@online.de) 4Faculty of Chemical Technology, University of
Pardubice, 53002 Pardubice, Czech Republic (karel.ventura@upce.cz)
Introduction: The Ries crater impact structure in
Germany measuring about 25 km in diameter, formed
almost 15 million years ago in the Upper Miocene. In
the early seventies, when the Ries impact origin began
to replace the earlier volcanic explosion theory among
most geologists, research results of the reputable Ba-
varian geologist Erwin Rutte caused quite a stir, be-
cause they described the Ries (and Steinheim) impact
event as much more far-reaching than the traditional
German impact researchers believed at that time [1, 2
and references therein]. This was followed by a strong
recognition in the geological community, replaced by a
vehement rejection of the whole hypothesis and a sub-
sequent ignorance and oblivion. Here we report on a
resumption of research on a particularly puzzling com-
ponent of this then completely new impact hypothesis,
which is put in a new light with new findings.
Alemonite: First described by Rutte in 1971 [1],
alemonite originated during the Ries impact event,
when pressure, temperature and delivery of vast quan-
tities of cosmic silica initiated heavy fracturing and
melting of local Jurassic, Cretaceous and crystalline
rocks of various lithologies thus forming a variety-rich
and characteristic new rock [2]. Depending on the
source rocks, breccias and silicifications of various
whole rock units were formed, which led Rutte to
speak of alemonitization, which should have affected
entire regions with a concentration in the Altmühlalb
and Upper Palatinate, and some extension to South
Bohemia and Austria. Parallel and closely connected
with the alemonitization, whole strewn fields of small-
er meteorite craters should have been created by the
impact of projectiles accompanying the Ries impact.
From an impact-related point of view, the alemonites
were a very special phenomenon in the narrower sense.
They appear as fist- and head-sized cobbles up to me-
ter-sized blocks, forming real strewn fields (Fig. 1).
These are polymictic breccias with features (according
to Rutte) of an impact melt rock with shock effects. At
that time it is not clear, what has not changed until
today, that the "melt rock mass" and the embedded
breccia components of all primary lithologies continu-
ously consist of >98% silica,
Disputed: The new hypothesis, which was not a
sudden invention but based on years of extensive and
meticulous field work with a dozen of students, pro-
voked protest and absolute rejection from the Bavarian
official geologic survey. All postulated smaller craters
were generally dismissed as karst phenomena. The
polymictic breccias evidencing high PT should have
been formed in a weathering period with warm climat-
ic conditions or in case of water level fluctuations of
freshwater lakes. Even today, Bavarian official geolo-
gists (LfU) insists on these explanations [3].
Forgotten: At that time a few members of the Ries
crater research group undertook a short field trip into
the new area postulated by Rutte, and the rejection by
the German impact researchers followed on the foot. A
logical consequence of the rejection and disregard of
official geology and German impact research was best
to forget the whole thing. Rutte continued his work
with a number of publications, but what was ultimately
a decisive weakness of his research was that not a sin-
gle one of his partly impressive publications had ap-
peared internationally in English but all in German.
Revitalized: Author M.M., without knowing the
Ries history and related alemonites, revitalized the
Rutte hypothesis, when he recently asked for the for-
mation of a special kind of silicified rocks extended in
the Czech Republic, which in the population are in
general called sunstones. For author K.E. the sunstones
sent to him proved to be more or less an exact copy of
the brecciated alemonites as described by Rutte sug-
gesting a possible interrelation between both occur-
rences (Fig. 1) as exemplified in the follwing.
Alemonite and sunstone samples from the field:
The sunstones found in the Czech Republic, which are
absolutely similar to Rutte's alemonites when picked
up quickly (see the later discussion on silcretes), have
identical properties even on closer inspection (Fig. 2).
This is the brecciated, sometimes diamictic, character,
the mostly smooth rounded surface as well as its partly
pronounced regmaglyptic sculpture (Fig. 2), as it is
known from ablation processes of meteorites. The
regmaglypts suggest at least superficial melt or strong
plasticity and aerodynamic deformation. The identity
of Rutte's alemonites and the sunstones goes so far that
hardness tests on the cut surfaces of many samples
show a uniform Mohs hardness of 7.5, and this without
1370.pdf50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132)
any noticeable offset across the entire cut surface by
matrix and components.
Fig. 2. Alemonites (DE) and sunstones (CZ) from the
field. Left: Whole samples. Note the meteorite-like
regmaglyptic surface sculpture (see text). Middle: Pol-
ished cut of CZ and DE breccias. Right: Polished cut
of sunstone (CZ) and alemonite (DE) polymictic brec-
cias. Note breccia generations (arrows; three in the CZ
breccia).
The polymictic breccia character becomes particu-
larly clear in the cut of the cobbles and boulders from
both occurences (Fig. 2), whereby particularly the fre-
quently occurring breccia generations (breccias-within-
breccias) are noticeable, therefore, because such brec-
cia generations are practically unknown in normal geo-
logical processes but represent a characteristic of im-
pact processes with rapidly successive phases of exca-
vation, ejection, landing of ejecta with mixing with
local material and finally movements of crater modifi-
cation.
Thin sections, SEM-EDS, X-ray diffraction Shat-
tered quartz grains down to microscopic size (SEM-
EDS, Fig. 3), quartzite fragments, but also well-
rounded quartzite pebbles occur in a microcrystalline
and/or amorphous silica groundmass. From X-ray dif-
fraction measurements of sunstones the amorphous
component yields a few, up to ten percent beside prac-
tically pure hexagonal quartz. This points to beta
quartz, more correctly to pseudomorphs of alpha
quartz after beta quartz. Therefore these sunstones
must have experienced temperatures >573°C for the
alpha to beta quartz transition.
Fig. 3. Preliminary SEM-EDS. Left: Sunstone
breccia in SEM image. Right: EDS spectrum of quartz
fragment in glass (?) matrix.
Matrix-within-matrix flow texture is frequently ac-
componied by strong gradation of quartz fragments.
Glass inclusions and glass veinlets are common (Fig.
4). Shock metamorphism already reported by Rutte is
found in the new alemonites and also in the sunstone
samples, however mostly on a moderate level (PFs,
PDFs in quartz; Fig. 4) and not very abundant.
Discussion: The Czech sunstones In general, the
Czech sunstones are regarded as silcretes (silicified,
hardened, conglomeratic, crust-like soil formations),
which have formed especially on the territory of the
Bohemian Massif (with the distinction of Elbe and
Rudná types) and are of unclear age and origin [4-6].
Fig. 4. Shock effects (multiple sets of PFs and PDFs)
in alemonites (DE) and sunstones (CZ). Photomicro-
graphs, crossed polarizers. - To the right: Glass particle
with schlieren and glass veinlet cutting through a
quartz fragment. Plane light.
This interpretation may be correct in many cases,
but confusions may occur without precise analyses.
The Czech sunstone alemonites differ in spite of some
common characteristics with silcrets in particular by
polymictic breccias shattered down into the micro
range, up to three breccia generations in only one small
sample, glass inclusions, moderate shock effects, and
hexagonal beta quartz that forms at temperatures >573
°C. According to generally accepted impact criteria,
these features, phenomenology and internal texture
speak clearly for the character of meteorite impact
breccias, as is the case with Rutte's alemonite breccias.
According to Rutte's research in Bavaria, the alemo-
nitizations occurred at the same time as the Ries crater
event whereby the alemonites are by no means distal
ejecta but must have originated more or less locally,
which should apply also to the far reaching Czech sun-
stone/alemonites, for which a possible Miocene age is
discussed [4].
Conclusions: The question about the process of the
mysterious formation of the alemonite breccias is not
answered here either, but urges us to look at the Ries
crater and its formation with new eyes in the sense of
Rutte, posthumously bringing justice to this great Ba-
varian geologist. It shows that the spontaneous rejec-
tion at that time by the German Ries impact research
group and the regional official geology was short-
sighted, and, in order to remain with the Ries crater
and the probable connection with the alemonites, it
underlines that phenomena can occur with large im-
pacts, which are still enigmatic and inexplicable. We
will continue to investigate the alemonite phenomenon.
References: [1] Rutte, E. (1971) Geoforum, 7, 84-
92. [2] Rutte, E. (2003) Land der neuen Steine, 110 p.,
Regensburg (Univ.Verlag). [3] Eichhorn, R. et al.
(2012) Nicht von dieser Welt - Bayerns Meteorite
(LFU, ed.) , 126 p. [4] Cílec, V. http://old.speleo.cz/soub-
ory/speleo/sp20/silkrety.htm [5] Cílek V. & Bednářová J.
(1993) Čes.kras (Beroun), XVIII: 4-13 [6] Musil, R. et
al. (1993) GEO program, 55-65, Brno. [4-6] in Czech.
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