Hamburg        42°26.82’N, 83°50.5’W

Michigan, United States

Confirmed fall: 2018 Jan 16

Classification: Ordinary chondrite (H4)

History: On 16 January 2018 around 20:10 EST, a fireball was observed and reported by hundreds of people from seven states. The fireball was recorded by multiple security cameras and registered as a 2.0 magnitude earthquake. Mike Hankey (AmMS) calculated the trajectory within one hour. A strewnfield map was produced by Marc Fries (JSC) using weather radar data from radar reflections of falling meteorites. The first fragment was found on 18 January 2018 at 7:50 EST by Robert Ward on Strawberry Lake near Hamburg, Michigan. Five other masses, ranging from 17 to 102.6 g, were found later the same day by Ward, Larry Atkins, and Darryl Landry on Strawberry and Bass Lakes. Thirteen additional pieces were found within two weeks of the fall.

Physical characteristics: Most stones are fully covered by fusion crust.

Petrography: Metal-rich texture typical of H chondrites is apparent on cut surfaces. The metal volume estimate is 9% based on an Fe EDS map. Chondrules are visible in polished section. The average chondrule diameter is 0.4±0.2 mm (N=26). Several chondrules are well-defined and have sharp boundaries. Pyroxenes are mostly orthopyroxene and less abundant clinopyroxene as determined with Raman spectroscopy. Feldspar grains vary in size and measure 3.4±2.2 μm (n=64) in a representative field of view. Chromites are impact fractured. No chromite veinlets nor opaque veins are observed within the meteorite. Phosphates account for about 0.5% of the meteorite and occur mainly as merrillite (0.4%) and apatite (0.1%). In a representative field of view, grain sizes for merrillite average around 100 µm and range from <1 µm up to 430 µm (n=37); apatite ranges from 70 µm to 310 µm with an average of 150 µm (n=8). The meteorite appears very weakly shocked. Melt veins (Fe-sulfide) occur only in close proximity to the fusion crust.

Geochemistry: Mineral Compositions and geochemistry: Olivine Fa_18.7±0.7 (N=34). The average composition of Ca-poor px is Fs_16.3±0.4Wo_1.3±0.1 (n=80). Feldspar is present with an average composition of An_14.0±4.0Ab_81.1±3.0 Or_4.8±1.3 (n=13). Chromite: TiO₂=2.0±0.4 wt% V₂O₃=0.8±0.2 wt% (N=25). Apatite contains about 5 wt% Cl and <1 wt% F.

Classification: The petrology, mineral chemistry and compositional hetereogeneity of the minerals listed is consistent with H4 chondrites. The meteorite is classified as H4, S2, W0.

Specimens: Type specimen 22.8 g and polished section at FMNH; 102.6 g specimen with Robert Ward; 44.5 g specimen with Terry Boudreaux.