Tocache        8°11.78’S, 76°28.64’W

San Martin, Peru

Confirmed fall: 1998 Jan 01

Classification: Ordinary chondrite (H5)

History: The meteorite fall was witnessed by Mr. Leodegario Tolentino Laiza and Mrs. Horacia Padilla Herrera in the Tocache District, Tocache Province, San Martín Department, Peru. According to the witnesses, the fall occurred between midnight and two in the morning of January 1, 1998. A fireball was observed in the sky and, within ", it exploded. Soon after, a humming sound, like a small plane, was heard and then two impacts on the ground were felt. In the following week, Mr. Leodegario found the 5140 g fragment on his coffee plantation, in a small crater 1 m deep by 50-80 cm in diameter in the clay soil. According to him, the meteorite had a smell that resembled something burned and with sulfur. The meteorite was kept in a shed of the property, being exposed to the high humidity of the region that is part of the Peruvian Amazon. In 2017, the fragment was acquired from the couple’s son, Mr. Willy Tolentino Padilla, by the Quimiosfera Laboratory at the Chemistry Institute of the University of São Paulo (USP) for study and classification.

Physical characteristics: The only fragment of the fall was acquired by the laboratory and weighed 5110 g, in addition to 30 g of fragments that were previously broken and sent by the owner. Thus, the final mass added up to 5140 g. The fragment was covered in about 80% of a dark-reddish fusion crust with different ° of oxidation. The exposed inner parts also have several rust colored spots of oxidized metal flakes. The fragment measured about 22 × 13 × 13 cm before the cut. One of the sides shows slight signs of orientation and, in one of the exposed inner parts, the meteorite shows a feature positively identified as a shatter cone. The conical and striated structure has 3 × 4 cm and was partially damaged by the action of the former owner during the removal of the 30 g of fragments that were first sent to the laboratory.

Petrography: Chondrule apparent diameter typically between 0.3 and 0.8 mm (mean 0.5 mm). Chondrules are not well defined. The chondrules represent around 60 to 70% of the area of the meteorite thin section. Most of the types seen are PO and POP, with RP appearing in lesser proportion, with no identified CAIs or AOAs. The Ol/Px proportion is around 80%/20%. More than 95% of the pyroxene crystals are orthopyroxenes, while 5% are clinopyroxenes. Olivine show light undulatory extinction, while virtually every pyroxene crystal shows strong undulatory properties. The pyroxene crystals commonly show both irregular and planar fractures. In contrast, the olivine crystals only show irregular fractures, while planar ones are rare. The metorite shows several long and thin melt veins (around 400 μm wide), some of them with small melt pockets and presence of melted metal and troilite flakes or even whole melt metal veins. The opaque phase makes up 11% of the meteorite volume (tomography), of which ~7-8% is kamacite/taenite, 3% is troilite and possibly 0.1 to 0.2% is chromite. The metal flakes have sizes varying between 0.1 and 1 mm (mean 0.3 mm), with some degree of connection between them being moderately common. Neumann lines can be seen on kamacite crystals and around 20 to 30% of the metal has already been oxidized. This generates an orange staining on the silicate phase around the metal flakes, being that areas near the surface show more oxidation than inner areas (F. Falco, USP).

Geochemistry: Mineral compositions and geochemistry: Olivine (Fa_20.1±0.8; N=82), low-Ca pyroxene (Fs_16.6±0.6Wo_1.3±0.7; N=60), high-Ca pyroxene (Fs_11.2Wo_25.7; N=1), feldspar (Ab_78.3±4.5An_15.7±6.4Or_5.9±4.7; N=7). MEV/EDS: troilite (Fe = 64.7±0.6 wt%, S = 35.5±0.6 wt%; N=2), kamacite (Ni = 7.2±1.5 wt%; N=2), taenite (Ni = 29.8±3.7 wt%; N=2), tetrataenite (Ni = 46.2±0.6 wt%; N=1), chromite (Cr/(Cr+Al): 0.88±0.06; N=4), zoned Cr-spinel (edge = Cr/(Cr+Al): 0.58±0.05, Mg/(Mg+Fe): 0.22±0.03, Ti: 0.5±0.1 wt%; N=3) (center = Cr/(Cr+Al): 0.29±0.04, Mg/(Mg+Fe): 0.40±0.03; N=3), apatite (Cl: 5.0±0.2 wt%, F: 1.2±0.2 wt%; N=1), ilmenite and merrillite (RAMAN).

Classification: Ordinary Chondrite (H5), S3, W2.

Specimens: Quimiosfera Laboratory - IQ/USP: 3320 g (main mass); Museo de Historia Natural - UNMSM: 131.6g; Type specimens: IGc/USP: 397.13g and 6 thin sections, MNRJ: 145.6 g and MCM: 7.4g and 2 thin sections.