Hradec Králové

Hradec Králové       50°18.03’N, 15°43.67’E

Královéhradecký, Czech Republic

Confirmed fall: 17 May 2016

Classification: Ordinary chondrite (LL5)

History: (P. Spurný, CzAS^[2]). A slow moving, -11.5 absolute magnitude, bolide was recorded photographically and photoelectrically by digital all-sky fireball observatories at three Czech stations of the European Fireball Network (other stations had bad weather) and by two web cameras of the Czech Hydrometeorological Institute on May 17, 2016, at 1:04:01.2-7.3 UT. Based on these instrumental data, precise results on atmospheric trajectory, heliocentric orbit, and fragmentation history were quickly determined. It was evident that this event terminated with a multiple meteorite fall and the impact area of possible meteorite masses was modeled. However, a systematic search was very complicated because the fall occurred in an agriculturally cultivated area during the high vegetation season. Nevertheless, the impact area was announced in the CzAS official press release and the public was asked for a help with the search. After dedicated search activities of several teams (including CzAS team) and individual hunters, one freshly looking meteorite was recovered by a private hunter in the predicted location for a given mass. It was found in the oil seed grape field just after the harvest on July 30, 2016 and the finder informed P. Spurný(CzAS) about his find in March 2017. The sample was immediately analyzed by J. Haloda (CzGS).

Physical characteristics: (P. Spurný, CzAS). Hradec Kralove is a single, 133 g, slightly wedge-shaped stone measuring approximately 6×3.5×2 cm with bulk density 3.23 g/cm3. About half of its surface is covered by a thick, black, primary fusion crust, where one side contains well-developed regmaglypts. The second half of its surface is covered by a very thin secondary crust signifying a break up of the meteoroid in the last moment of its ablation phase. Only a few small rusty spots are visible on its surface. One small 1.1 g fraction was chipped from this sample and was used for mineralogical/petrological analyses. Another 22.2 g was cut later and it serves as the repository mass (CzAS).

Petrography: (J. Haloda, CzGS^[3]), The meteorite shows only weakly defined chondrules; sizes vary from around 0.5 mm to 5 mm. Thin section shows a complete recrystallization of a fine-grained matrix. An undulose extinction of olivine and orthopyroxene and presence of irregular fractures indicate a very weak shock stage (S2).

Geochemistry: Mineral compositions and geochemistry: (J. Haloda, CzGS), Chondrule relicts consist mostly of olivine (Fa_25-33) mean Fa_29.7, Fa PMD 3.5%, n=50; low-Ca pyroxene (Fs_21-27Wo_0.8-2.4) mean Fs_24.0 Wo_1.7, Fs PMD 4.7%, Wo PMD 5.7%, n=50. Feldspar grains <10 mm, chromite, chlorapatite, troilite, kamacite and taenite are also present.

Classification: (J. Haloda, CzGS), Ordinary chondrite, LL5 (S2). Weathering grade W0

Specimens: Type specimen 22.2 g + 0.5 g, CzAS; the main mass (110 g) is with the finder (M. Maršík)