Spanish scientific Forum of Meteorites and Planetary Geology (since 1998) The Getafe rock (pseudometeorite)
Special thanks to José Martín
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 Getafe
cannot be catalogued as a meteorite.
Later on, Getafe was officially catalogued for our research group in 2002 as a pseudometeorite in the meteorite collection of the National Museum of Natural Science, Madrid (Spain). This contribution was also presented in the Iberian Congress of Meteorites and Planetary Geology
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Reports and scientific publications |
Selected information from publications |
Invited talks |
Paragenesis and mineral chemistry |
Geochemical (and isotopic) characteristics |
Cosmic ray records |
MAPS |
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Interesting
website about an unusual refractory material from Granada, Colorado (USA)
( by Neil B. Ray and Timothy C. Mullin) |
 Our
works have determined the mineral paragenesis and the geochemical (including
isotopic) features of the Getafe rock and that it cannot be catalogued
as a meteorite.
"...The only artificial material which presents some compositional similarities to the GR is a specific type of primary steelmaking slag: namely Electric Arc Furnace (EAF) slags. These EAF slags are crystalline solids, with the textural and chemical appearance of igneous rock, which have a high density (2.4 g/cm3 —approximately half that of GR—) and a compositional variability depending on the proportion in which components are artificially mixed. The mean composition of EAF slags is: CaO: 40.40; MgO: 3.70; SiO 2: 25.20; Al2O3: 4.80; FeO: 18.50; MnO: 6.50; TiO2: 0.30. The mineralogy of the steelmaking slags is characterized by the presence of di-and tricalcic silicates, ferrites, iron and manganese oxides and free CaO. In fact, free CaO (which is absent in the GR) is the main component which typifies the composition and industrial applications of this type of slag...". From Martinez-Frias et al (1999)
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Minerals were identified by XRD, transmitted and reflected light microscopy, SEM, and electron microprobe. The GR is made up of a fine grained matrix rich in silicates (mainly larnite and melilite, of gehlenite type) and oxides (mainly wustite and chromite) and inclusions of native iron metal. Minor grains displaying spinel and perovskite compositions (closely associated with melilite as a dark, apparently glassy ground mass), and minute grains of troilite, corundum, and native copper were also detected within the matrix.
Although it is difficult to establish a clear crystallization sequence, ore textures seem to reflect a combination of several processes which include: rapid cooling and rapid growth (quenching) from a liquid (as indicated by the presence of acicular, dendritic and spherulitic textures), varying proportions of melted and crystallized zones and some recrystallization. Apart from the individual textural characteristics of the different mineral phases which will be described below, the most peculiar texture of the GR involves chromite (or chromite-melilite) cores and flower-type wustite rims.
Specific PIXE probe analyses were also carried out on 18 spots (6 on iron, 2 metal?oxide (wustite) blebs, 7 melilites and 3 larnites). The PIXE data show that PGE and the rare earth elements (REE), are below detection limits (detection limits for Re, Os, Ir, Pt and Au are 20?40 ppm, and for La are 30 ppm in larnite, 80 ppm in melilite). From Martinez-Frias et al (1999)
Major, minor and trace elements (including REE) of the GR were determined by NAA, ICP-MS, ICP-AES, XRF and AAS. The bulk geochemical composition is rich in iron and calcium (Fe=18,57% and Ca=24,86%), (reflecting the mineral phases given above), Si (7,60%), Al (5,68%), Mn (4,41%), Mg (2,03%), Cr (0,97%) and Ti (0,34%). The refractory trace elements Zr, Nb, Sr and Ba are extremely high (20 x CI - 800 x CI) and Y, Ti and V are £ 10 x CI; Sc is low (0,2 x CI), and the light REE (La,Ce) are 40 x CI, while the heavy REE are less enriched (approx. 10 x CI). The Ni content is 18 ppm. Its chondrite-normalized REE distribution pattern indicates strong fractionation from LREE to HREE. The oxygen data plot on the terrestrial fractionation line. d 8O values of +16.3% and +15.6%, and d 17O values of 8.1% and 8.0% (rel. To SMOW), which are rather high. From Martinez-Frias et al (1999).
Cosmic-ray produced nuclides are excellent tracers for the exposure of rocks in space. As the cosmic ray flux at the location (~40° geomagnetic latitude, ~650 m above sea level) of Getafe is about three orders of magnitude lower than in interplanetary space, cosmic ray produced nuclides are expected to answer the question whether space exposure did occur. A pilot study showed essentially terrestrial atmospheric composition for the light noble gases with slight excesses of 21Ne and 40Ar. Therefore, a detailed study of a 388 mg sample of bulk material for all noble gas isotopic abundances was conducted using techniques developed for the study of surface exposure times of terrestrial rocks. Noble gases were released by stepwise heating the sample in a resistance-heated tantalum crucible. The evolved gases were cleaned on a titanium sponge getter and a SAES NP-10 and separated cryogenically. Xenon, krypton, and argon were adsorbed on a stainless steel frit at 77K and neon and helium were adsorbed on charcoal at 35K and 11K, respectively. All gases were analysed sequentially by static mass spectrometry using Daly and Faraday detectors on a customized VG5400. Air standards were used for calibration of sensitivities and mass discrimination. An aluminum foil was analyzed for background correction using the same procedures as for the sample.
Krypton and xenon are consistent with atmospheric abundances and are not given. Neon isotopic ratios of all temperature steps are (within 2.3s) equivalent to air except for the 22Ne/20Ne in the 1,100°C fraction that is higher. The slight 21Ne-excess, (2.12±0.81)·106atoms/g, can be used to obtain only an upper limit for the space exposure time of the rock, since some excess may also be due to the 18O(a,n)21Ne reaction. With this assumption and using average 21Ne-production rates for space exposure, P21 = 30,000 atoms/gram/year, we calculate a space exposure age of <97 years. Alternatively, if we consider only a terrestrial history, and adopting the cosmic ray production rate of 21Ne in terrestrial silicon, P21 = 45 atoms/gram Si/year, corrected for latitude and altitude, P21 = 74 atoms/gram Si/year, and the silicon abundance (7.6%), we obtain a terrestrial surface exposure age of <520,000 years. Using modeled terrestrial surface exposure 21Ne-production rates taking into account contributions from Na, Mg, Al, Si, Ca, Fe, we obtain P21 = 19 atoms/gram/year, and derive an age of <149’000 years. All these ages are upper limits because a small 22Ne excess (1,100°C fraction) suggests either a nucleogenic contribution from the 19F(a,n)22Ne reaction or a trapped Ne signature distinct from atmospheric Ne.
The argon concentration (36Ar = 8.65·10-9cm3STP/g) and isotope ratios, which barely exceed the atmospheric value, imply a limit of radiogenic 40Ar < 2.34·10-8cm3STP/g, which coupled to the measured potassium abundance (166 ppm) yields a maximum gas retention age of 27.6·106 years. Minor variations are also observed in the 38Ar/36Ar ratios and indicate a nucleogenic component or fractionation effects.
The 14C activity (T1/2 = 5730 a) was determined in a bulk powder sample and also in the acid soluble phase and in the residue of the treated sample. The bulk sample has a C concentration of 0.38% (by weight) and a 14C activity of (1.037±0.009) times modern terrestrial C, or 51.6±0.5 dpm/kg. The acid-soluble phase revealed a fraction of (1.079±0.006) and the residue one of (0.870±0.008) times modern terrestrial. If interpreted as an activity induced by cosmic rays in space, this would correspond to a close to saturation activity. However, the activities observed in different phases (acid soluble vs. acid insoluble) are very different and do not agree with typical activities induced in space.
To check the possibility that cosmic-ray produced Ne could have been lost from the rock, 10Be in the bulk rock was also measured; the activity was extremely low with an upper limit of 0.01 dpm/kg. Therefore, both nuclides, stable 21Ne and radioactive 10Be allow upper limits for the space exposure time of 103 years. A possible interpretation could be that the carbon is terrestrial material. Carbon with a “fraction of modern” of 1.03 to 1.08 can only have been formed in the period of 1955-1958 AD and not earlier or more recently. From Martinez-Frias et al (1999
| In 1994 a moving car and its driver,
on a highway in southern Madrid (Getafe), were struck by a falling rock.
Eighty-one additional fragments (total weight : 55.926 kg) were later recovered,
which all pointed towards a meteorite fall. A study of the composition
of this object revealed an ultrarefractory material displaying a most unusual
chemical make-up which differs from any known meteorite class, and for
some elements and minerals approaches the composition of CAI (Ca-Al-rich
inclusions in chondrites). A study of some cosmic-ray- produced stable
and radioactive nuclides indicates: a) space and terrestrial exposure ages
which do not exceed 1,000 and 520,000 years, respectively; b) the presence
of a small 22Ne excess (1100ºC fraction), which suggests either a
nucleogenic contribution from the 19F(?,n)22Ne reaction or a trapped Ne
signature distinct from atmospheric Ne, and c) the existence of minor variations
in the 38Ar/36Ar ratios also indicating a nucleogenic component or fractionation
effects. 14C data are consistent with “modern” carbon originated in the
period 1955-1958 and not earlier or more recently. The possibility that
Getafe could have a man-made origin (i.e. ceramic and refractory tiles,
industrial slag) is also considered.
"...In short, it is difficult to conclude, without reasonable doubt, what the real origin of the Getafe rock is. Could it be an unusual (and unique) CAI-type extraterrestrial rock, which underwent significant isotopic fractionation, and which, despite this, still preserves remains of the nucleogenic contribution such as those reflected by the small 22Ne excess (1100ºC fraction), and the minor variations of the 38Ar/36Ar ratios?..." This would support the theory of CAI accumulation in kilometre-sized bodies (piñatas) with relatively stable orbits, during the first differentiation stages of the primitive solar nebula (Boss 1995). In fact, this author points out, citing W.R. Skinner, that the large CAI-filled piñatas would have to be broken apart 10 Ma later, releasing the CAIs for incorporation into chondritic bodies...." From Martínez-Frías et al (1999) Revista de Metalurgia 35: 308-315 Acknowledgements : This research was carried out thanks to the financial backing of the Spanish CSIC and CICYT. Special thanks to Prof. Alan P. Boss and K. Marti, the 'Museo Nacional de Ciencias Naturales' de Madrid, J.M. Martin and Madrid Directo. |
(caídd, el 1994 |
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INFORMATION FROM SOME SELECTED PUBLICACIONES
Martinez-Frias, J. (1998) La roca de Getafe: trayectoria de caída, efectos del impacto y marcadores morfotexturales de vuelo. Geogaceta 25: 215-218.
ABSTRACT
On 21st June, 1994, at approximately 12 noon local time, a rock, weighing 1.417 kg and measuring 18 x 8.5 x 8 cm, struck a car, which was travelling south on the Madrid-Andalucía road (Getafe city, south Madrid). This area is open country made up of marls, gypsum beds and claystones, without bridges or other high places from which the rock could have been thrown. The incident was spectacular. The rock impacted the car at about 30??from the horizontal and hit the steering wheel and the driver's right hand with such force that the steel wheel was deformed. This work constitutes the first contribution on the study of the Getafe rock (GR), displaying a detailed analyses of the trajectory of fall, effects of impact and morphotextural evidence of flight. The GR is a semi-oriented specimen (apex angle 75°), with an external scoriaceous texture which resembles either an industrial slag or the highly vesicular "scoriaceous-type" micrometeorites (AM10 and M4) which were recovered in Antarctica. It does not appear to have fusion crust, although textural and colour differences exist between its external and internal parts. At least two different systems of friction striae as well as two types (milky and dark) of droplet-globules (100 ?m-500 ?m) were found scattered on its frontal, smooth surface. Some of these show presence of impact microcraters. Although the circumstances surrounding the fall are very well documented and despite clear evidence of flight were found, the GR does not exactly match any of the previously classified meteorites nor any known rocks (terrestrial or extraterrestrial).
Key Words: Getafe rock, fall, impact,
evidence of flight, Madrid
Martinez-Frias, J., Weigel, A., Marti, K.,
Boyd, T, Wilson, G.H. & Jull, T. (1999). The Getafe rock: Fall,composition
and cosmic ray records of an unusual ultrarefractory scoriaceous material.
Revista de Metalurgia 35: 308-315.
ABSTRACT
In 1994 a moving car and its driver, on a highway in southern Madrid (Getafe), were struck by a falling rock. Eighty-one additional fragments (total weight : 55.926 kg) were later recovered, which all pointed towards a meteorite fall. A study of the composition of this object revealed an ultrarefractory material displaying a most unusual chemical make-up which differs from any known meteorite class, and for some elements and minerals approaches the composition of CAI (Ca-Al-rich inclusions in chondrites). A study of some cosmic-ray-produced stable and radioactive nuclides indicates: a) space and terrestrial exposure ages which do not exceed 1,000 and 520,000 years, respectively; b) the presence of a small 22Ne excess (1100ºC fraction), which suggests either a nucleogenic contribution from the 19F(?,n)22Ne reaction or a trapped Ne signature distinct from atmospheric Ne, and c) the existence of minor variations in the 38Ar/36Ar ratios also indicating a nucleogenic component or fractionation effects. 14C data are consistent with “modern” carbon originated in the period 1955-1958 and not earlier or more recently. The possibility that Getafe could have a man-made origin (i.e. ceramic and refractory tiles, industrial slag) is also considered.
Key Words: Getafe rock, fall, composition,
cosmic ray records, meteorite, slag, Madrid, Spain.
Martínez-Frías, J., Benito, R., Wilson, G., Delgado, A., Boyd, T & Marti, K. (2001) Analysis and chemical composition of larnite-rich ultrarefractory materials. International Conference on Advances in Materials and Processing Technologies, Madrid.
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Larnite ( b-Ca2SiO4) is a very rare and little known compound in nature. It forms part --along with forsterite (Mg2SiO4), fayalite (Fe2SiO4), and tephroite (Mn2SiO4)--, of the monticellite and knebelite series (general group of olivine). However, despite its scarcity, larnite has been found in different natural settings, almost always under thermodynamic conditions of around 0.2-1 kbar and 1,000 to 1,100C. Larnite can also be artificially formed, especially during the synthesis of high technology refractory and ceramics materials, and as a mineral component of some industrial slags. Typical portland cements are mixtures of tricalcium silicate (3CaO SiO2), tricalcium aluminate (3CaO Al2O3), and dicalcium silicate (2CaO SiO2), in varying proportions, together with small amounts of magnesium and iron compounds. This work displays the analysis and compositional properties of larnite-rich ultrarefractory materials, cataloged as possible meteorite specimens (Getafe rock, Fig. 1), from the collection of the "Museo Nacional de Ciencias Naturales" (Madrid). Larnite is associated with metal oxides and sulfides, native iron and copper, and calcium-aluminium silicates (Fig. 2). Bulk chemical composition was determined by XRF (specific standards and analytical routines were designed, Table 1 and Fig. 3). Minor and trace elements (including rare earths) were analyzed by the combination of NAA, ICP-MS and ICP-AES. These ultrarefractory materials are rich in iron and calcium (Table 2). Larnite occurs as imperfectly developed tabular crystals, mainly displaying rhombic shapes of around 25 x 35 mm. SEM and microprobe analyses (Fig. 4) indicate that its chemical composition closely matches the theoretical formula (x = Ca1.96 Si0.98 O4), although significant amounts of Al (Al0.19-Al0.54), Fe (Fe0.01-Fe0.14), Mn (Mn0.01-Mn0.03) and Mg (Mg0.01-Mg0.02) have also been detected in some crystals. PIXE analyses display high Fe and Ba values, ranging from 3.9 Wt % to 8.4 Wt %, and from 1058 ppm to 1530 ppm, respectively. |
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Further information:
Jesús
Martínez-Frías
