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Okechobee

L4
standby for okechobee photo
Found 1916
26° 41′ N., 80° 48′ W. Fragments weighing ~1 kg were brought up in a net about three-quarters of a mile from the shore of Lake Okeechobee. This is one of only four meteorites found in Florida, all of them of the stony type. The above specimen is a 0.87 g crusted fragment.

Due in part to the intense temperature and moisture conditions in the state of Florida, only four meteorites have been found there to date, in addition to two recovered falls. Besides Okechobee, an H4 stone weighing 502 g was plowed up in Eustis, a 41.8 kg H5 stone was found in Bonita Springs, and a 10.9 kg H5 stone was found near Grayton Beach. In 2004, November 8 at 6:15 P.M., Orlando resident Donna Shuford heard a meteorite bounce off her car and hit the side of her house. Fragments composing an ~180 g eucrite were recovered. In 2016, January 24 at 10:27 A.M., numerous eyewitnesses observed a bright fireball over northern Florida near the Osceola National Forest. Utilizing radar images from several stations, a group of hunters successfully plotted the fall site and recovered 8 stones over many weeks having a combined weight of 1,099.6 g. The L6 chondrite fell within a forested wetlands region delimiting a strewn field of approximately 5 miles × 1 mile.

Although the correct spelling of this Florida lake location is Okeechobee, the incorrect spelling initially used in the Catalogue of Meteorites of The Natural History Museum, London, as well as in the Meteoritical Bulletin Database is followed here. The correct spelling of this find location (more accurately, the nearest post office to the find location) has been included as a synonym in the Meteoritical Bulletin Database.


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Park Forest

L5 fragmental breccia
standby for park forest photo
Fell in 2003, March 26 at 11:50 P.M.
41° 29′ 05′ N., 87° 40′ 45′ W.

As midnight neared, ending the last Wednesday of March, 2003, a terrific fireball passed overhead on its long approach path. Following a SSW to NNE trajectory, the fireball put on a fiery display for residents of several states including Missouri, Illinois, Indiana, Michigan, and Ohio, ultimately delivering sonic detonations as multiple fragmentation events occurred at altitudes of 37, 29, and 22 km. Hundreds of fragments ended their journey in the southern suburbs of Chicago, showering the towns of Crete, Park Forest, and Olympia Fields with stones weighing from a few grams to 5.26 kg. Many of these fragments impacted cars, homes, lawns, sidewalks, streets, and even the local Fire Station, giving many unsuspecting residents an opportunity to recover a fresh meteorite—and others an opportunity to repair their damaged windows, roofs, and other structures.

Joining these resident ‘meteorite hunters’ were some cosmochemists from local institutions, including the University of Chicago, the Chicago Field Museum, and the Argonne National Laboratory. Among the many meteorite collectors and dealers who traveled to the fall location was Steve Arnold (International Meteorite Brokerage; ‘Meteorite Men’), along with his wife Qynne and two young daughters Kelsey and Lauren. All of the Arnold’s found meteorites during their trip—the first ever meteorite finds for Qynne, Kelsey and Lauren. standby for arnold family photo The Park Forest meteorite shown at the top of the page was one of several found by Lauren, and it was subsequently put up for sale via eBay auction. The story behind her find, written by Lauren herself, inspired my own bid—but in the end, I lost out to fellow collector Mike Fowler. Remarkably, three years later, this 3.5 g specimen is in the Weir Collection thanks to Mike’s generosity. Lauren’s personal account of the successful Arnold Family meteorite expedition follows:

‘Hi, my name is Lauren Arnold, I’m 11 years old. My Dad has been in the meteorite business my whole life, but until now I have never had a chance to hunt meteorites with him. Several weeks ago a big meteorite broke up and landed all over Chicago and my Dad went up to find some. He found a lot of them. So on his third trip to Chicago, my sister, my Mom and I talked him into taking us with him.

We made a deal that we had to keep our first meteorite we found, but we could sell the others. After getting to the motel the first day, we went to Burger King and both my sister and I got a Kid’s Meal, and guess what was the toy in them? A huge meteor! It came with a Superman Doll and a comic book. My Dad was so excited, and he read the comic book to us and it was about Superman finding a bunch of meteors after lunch. Dad told us ‘You know what that means don’t you? It is a sign that we are going to find a bunch of meteorites today.’

Well I found two that day, my sister found one and so did my Mom. The next couple of days we each found several more. We are all keeping our first ones, but we are selling the rest. Well, my Dad is selling them for us. But we get to keep the money! So bid real high because these are special. Oh, and we went back to Burger King that night and bought some more of the Kid’s Meal toys, so you also get one free included with each of our special meteorites we are selling if you are lucky enough to be the high bidder. I hope the toy brings you as much luck as it did us.’

standby for superman photo
Burger King Superman-Meteor Kid’s Meal toy

Park Forest was analyzed and classified at the University of Chicago (S. Simon), the Field Museum of Natural History (M. Wadhwa), and the Planetary Studies Foundation (P. Sipiera). Park Forest has olivine Fa and pyroxene Fs contents consistent with the L-group ordinary chondrites; O-isotopic ratios also confirm this classification (Simon et al., 2004). In accord with the scheme of Van Schmus and Wood, Park Forest is classified as a petrologic type 5. Park Forest is a strongly shocked (S5) monomict breccia consisting of light gray clasts within a darker matrix. It contains scattered FeNi-metal flakes throughout, while FeS veins occur only in the dark lithology, which is considered to be derived from the light lithology through impact shock processes that mobilized sulfides.

standby park forest lithologies photo
Park Forest stone exhibiting both light and dark lithologies
Photo courtesy of The University of Chicago News Office
Orbital, velocity, trajectory and pre-atmospheric mass data of the Park Forest bolide were obtained from U.S. Department of Energy and Department of Defense satellites, with additional information supplied by ground-based video camera and seismic and acoustic instruments (Brown et al., 2004). Satellite data indicate that the meteoroid’s entry velocity fell from an initial maximum of ~20 km/sec above 60 km, to ~14 km/sec at lower altitudes. Seismic and acoustic measurements infer a total energy equivalent to ~0.4–0.5 kilotonnes of TNT. This is an Apollo-type asteroid with a heliocentric orbit and an aphelion that likely coincides with the 3:1 mean-motion resonance with Jupiter at 2.50 AU.

Cosmogenic radionuclide measurements indicate that the pre-atmospheric mass of Park Forest was between 900 and 7,000 kg, with the higher value being consistent with a model based on porosity. Based on a gross fragmentation model, it could be argued that Park Forest was initially a meteoroid ~2 m in diameter with a pre-atmospheric mass of ~14,000 kg. In their compilation of measurement techniques, Brown et al. (2004) derived an initial pre-atmospheric mass estimate of 11,000 (±3,000) kg and a diameter of 1.8 m. Meier et al. (2017) conducted a re-analysis of cosmogenic radionuclides and noble gas abundances for Park Forest, and their new data, consistent with that of two established models, provided the following results:

  • a pre-atmospheric mass of 1,730–5,870 kg
  • a pre-atmospheric diameter of 1.06–1.76 m
  • a porosity of 0–40%
  • a density of 2.0–3.4 g cm–3

In addition, Meier et al. (2017) determined that the radiogenic gas retention ages ([U, Th]–He and K–Ar) for Park Forest are consistent with that of the catastrophic disruption of the L chondrite parent body, an event dated at 470 (±6) m.y. ago as attested by the abundance of fossil L chondrites and associated chromite grains recovered from Mid-Ordovician limestone quarries in Sweden and other countries (see the Beenham page for more information). Meier and Welten (2014) determined that Park Forest lacks solar wind noble gases, which indicates it is not a regolith breccia but is instead a fragmental breccia. They determined a 21Ne-based CRE age of ~17 m.y., and found that various radiometric chronometers had been reset in the relatively recent past. Meier et al. (2017) conducted a re-analysis of the cosmogenic noble gases for Park Forest, and their results gave a CRE age of 12 (±1) m.y. based on 3He, and 14 (±2) m.y. based on 21Ne and 38Ar.

Park Forest is one of a growing number of meteorites with a precisely calculated orbit (e.g., Pribram, Innisfree, Lost City, Peekskill, Neuschwanstein, Morávka, Tagish Lake, Novato). Meier et al. (2017) assert that the location of the L chondrite parent body at the time of breakup was near the Jupiter 5:2 mean motion resonance (signifying the ratio between the orbital period of Jupiter and that of an asteroid) from which rapid delivery from the inner asteroid belt to an Earth-crossing orbit could be attained, consistent with the CRE age calculated for the fossil L chondrites recovered from mid-Ordovician limestone quarries. Based on spectrographic and mineralogical data for more than 1,000 near-Earth asteroids, Binzel et al. (2016) determined the probable main belt source region for each of the ordinary chondrite groups (see diagram below). standby for resonance diagram
Diagram credit: Binzel et al., 47th LPSC, #1352 (2016) Thereafter, L chondrite material would have been delivered to the more efficient, albeit slower, 3:1 resonance (and the less important ν6 secular resonance) where transfer to Earth occurred over an extended period of millions of years. The S-type asteroids of the Gefion family have been historically considered a probable source for the L chondrites. However, in consideration of such factors as pre-breakup size, breakup age, and shock-darkening history of the parent asteroid, Meier et al. (2017) contend that the Ino asteroid family may be a more plausible source (see the Beenham page for further details). Utilizing surface thermal conductivity estimates for the Park Forest meteoroid, they calculated its possible orbital evolution following its ejection ~14 m.y. ago. They conclude that its delivery to Earth was either directly through the 5:2 resonance or that it migrated to the 3:1 resonance buried at a significant shielding depth within a larger meteoroid. standby for park forest orbit diagram
Diagram credit: Meier et al., MAPS, vol. 52, p. 1563 (2017)
‘Park Forest (L5) and the asteroidal source of shocked L chondrites’
(http://dx.doi.org/10.1111/maps.12874)
The total recovered weight of the Park Forest meteorite is only ~30 kg out of a predicted ground fall mass of up to 150 kg. The specimen shown at the top is a 3.53 g half stone which was broken upon impact; dark shock veins can be seen traversing the light gray lithology. The photo below is an excellent petrographic thin section micrograph of Park Forest shown courtesy of Peter Marmet. standby for park forest ts photo
click on image for a magnified view
Photo courtesy of Peter Marmet


For additional information on the Park Forest fall, read the PSRD article by Linda M.V. Martel—’Meteorite Shower in Park Forest, Illinois‘, Aug 2004.


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NWA 4150

L impact-melt rock
(H/L6 impact-melt clast in MetBull 90)
(H/L6-melt rock in MetBull Database)

standby for northwest africa 4150 photo
Purchased before 2006
no coordinates recorded Two pieces of a single stone weighing together 436.4 g were found in Northwest Africa and sold in Erfoud, Morocco to meteorite collector C. Anger of Austromet. A sample was submitted for analysis and classification to the Museum für Naturkunde (A. Greshake and M. Kurz), and it was initially determined that NWA 4150 is a unique melt lithology belonging to the transitional H/L-chondrite group. This initial classification has been revised based on continued study (Wittmann et al., 2011).

Northwest Africa 4150 has an average olivine Fa value of 24.1 and an average pyroxene Fs value of 19.9, values which are in the range of the L-chondrite group. The metal abundance of 5% matches that of L chondrites, and the concentration of Co in kamacite matches that group as well. A wide variety of chondrules are represented over a much reduced surface area due to the chondritic melt, and they have average dimensions indistinguishable from those of L chondrites. Along with a quenched melt mesostasis, the chondrules and microcrystalline chondrule fragments exhibit an excellent state of preservation, and surviving lithic clasts indicate a petrologic type of L3–L4 (Wittmann et al., 2011). An Fe–S–Si melt covers a significant area, with a cooling rate estimated to be 0.05°C per year, similar to that of L5 Cat Mountain, and corresponding to the metallographic cooling rate at a depth of 1 km. Shock features are prevalent in chondrule fragments, including undulous extinction, planar fractures, mosaicism, and brown olivine. The crystallized impact-melt component contains rounded metal and sulfide particles and aggregates very similar in shape to those in L6 Wickenburg. It is suggested that NWA 4150 formed within a thick breccia lens of a crater measuring 5–7 km in diameter.

It might be a reasonable assumption that the L impact-melt rock NWA 4150 could be paired with the five member pairing group comprising NWA 4152–4156 which were initially classified as H/L6 chondrites, especially considering that all were found at virtually the same location in the same timeframe, purchased by the same collector, submitted to the same classification lab, and assigned virtually consecutive NWA-series numbers. Moreover, similar scenarios have occurred before, in which a very small percentage of shock-melted stones were discovered associated with a majority of non-melted stones of a common fall, e.g., Gao-Guenie. Nevertheless, there are some petrographic features of NWA 4150 that might be inconsistent with such a pairing: its weathering grade of W0/1 is significantly lower than that of the NWA pairing group (W2–4), and its impact melt features reflect a much greater shock event than that commensurate with the NWA pairing group (S3–4). Further analysis is required to make a conclusion on their pairing status.

Another important factor relevant to the pairing question is the olivine Fa content that characterizes NWA 4150 (Fa24.1) compared to that of the NWA pairing group (Fa19.920.6). A recent study by Rubin et al. (2008), addresses the question of how the oxidation state of ordinary chondrites (represented by the mean olivine Fa value) varies over different size scales, and this may shed further light on the question of pairing. They found that the Fa values for the chondrites studied were heterogeneous on km-sized scales and above, but homogenous on meter-sized scales and below. It could be inferred that the Fa values of all stones that are derived from a single multi-fragmented meteoroid should all be identical, and therefore, the difference in Fa values between the L impact-melt rock NWA 4150 and the H/L6-NWA pairing group is inconsistent with their pairing.

The oxygen isotopic composition of NWA 4150 and its possible pairing group of NWA 4152–4156 will help establish their correct groupings. In addition, K–Ar data will be utilized to provide the age of impact. The photo of NWA 4150 shown above is a 3.21 g end section acquired from Christian Anger which exhibits a ring-shaped, metallic-melt swirl pattern in the upper left corner. Thank you dearly departed friend.


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NWA 2798

L3.2
northwest africa 2798 photo
Purchased 2005
no coordinates recorded Three conjoint fragments of an unequilibrated chondrite, having a combined weight of 1,805 g, were found in the Sahara Desert and sold to G. Hupé in Erfoud, Morocco. This meteorite was analyzed and classified at Northern Arizona University (J. Wittke and T. Bunch) as an L-type ordinary chondrite.

A new petrologic scheme that is more discriminating at the lowest metamorphic stages, those associated with the highly unequilibrated chondrites (3.0–3.2), was developed by Grossman (2004), Grossman and A. Brearley (2005), and Grossman (2008). This new classification scheme is based in part on a sensitive analytical technique utilizing the variation in the distribution of Cr in ferroan olivine, and it is virtually unaffected by the processes of terrestrial weathering and aqueous alteration. The petrologic scale of the new decimal system has been extended as follows:

3.00–3.05–3.10–3.15–3.2

For metamorphic types 3.00–3.03, chromite contents account for 0.3–0.5 wt% in the chondrite groups studied. While chromite contents in type 3.05–3.10 chondrites still reflect the lowest degrees of metamorphism, at a degree of metamorphism equivalent to type 3.15 the chromite abundance has declined to only 0.1–0.2 wt%. With metamorphic types of at least 3.2, the chromite abundance is mostly less than 0.1 wt%. Northwest Africa 2798 has a measured Cr content in olivine of 0.21 (±0.09) wt%, and with consideration of other parameters, has been assigned to subtype L3.2. It has a shock stage of S2 and a low weathering grade of W1. The specimen of NWA 2798 pictured above is a 6.13 g complete slice. standby for nwa 2798 main mass photo
Photo courtesy of Greg Hupé


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NWA 2797

L3.8
northwest africa 2797 photo
Purchased 2005
no coordinates recorded A single unequilibrated chondrite weighing 1,211 g was found in the Sahara Desert and sold to G. Hupé in Erfoud, Morocco. This chondrite was analyzed and classified at Northern Arizona University (J. Wittke and T. Bunch) and was assigned to subtype L3.8.

In their modeling of the accretion and impact history of ordinary chondrites, Blackburn et al. (2017) calculated the timing of the catastrophic disruption of the H- and L-chondrite parent bodies to be ~60 m.y. after CAIs. This timing is consistent with two competing dating techniques—U–Pb (and Hf–W) chronometry and metallographic cooling rates (Ni diffusion profiles in Fe-metal)—which record cooling associated with both an onion shell structure prior to disruption and a rubble pile after disruption, respectively. Utilizing Pb–phosphate age data, Edwards et al. (2017) determined that the H and L chondrites of petrologic type 6 (i.e., those located at the greatest depths in a concentrically zoned body) show a similar timing for closure of the Pb-phosphate system of ~60 m.y. after CAIs; this age reflects the occurrence of ubiquitous quenching during parent body disruption. Employing thermal models, they constrained the timing of accretion for the two parent bodies to 2.0–2.35 m.y. after CAIs, and they derived an estimate for the minimum size of the two parent bodies of ~275 km in diameter.

Northwest Africa 2797 has a shock stage of S2 and a weathering grade of W2. The specimen shown above is a 3.2 g partial slice.