Tishomingo is a singularly exotic meteorite, chemically and visually, an anomalous iron with the highest nickel content of any meteorite, and strange crystalline patterns from the bulk visual view here down to 200nm (see microscopy analysis in comment below). Subject to substantial scientific study, the research concludes that it is super-cold-forged steel, down to -75 to -200°C and required relatively rapid cooling and reheating events to generate its unusual metallurgy.
From the Christie’s auction house description: Tishomingo is unlike any other meteorite and is intrinsically among the most valuable of meteorites with a nickel content of approximately 32.5%. (The nickel content of most iron meteorites is less than 10%) As a result of its high nickel content, it exhibits a unique coarse martensitic structure. In the words of Dr. Vagn Buchwald in his legendary three volume standard source The Handbook of Iron Meteorites, “A similar structure is unknown in any other meteorite…Tishomingo is a very pure iron-nickel alloy. No carbides, phosphides or silicates were identified at all…Tishomingo is a unique meteorite, unrelated to any other meteorite.”
And from the Yang paper below, “Tishomingo is unique in that no other meteorite has preserved in its microstructure a detailed record of its low temperature history between -100 and 400 °C.”
Tishomingo was found by a 14-year old boy while bird hunting in 1965 in Oklahoma. As a result of Tishomingo’s high nickel “melt value”, it is among the most valuable meteorites known.
229 x 219 x 3mm (9 x 8.67 x 0.1 in.), 1,255g (2.75 lbs)
(b) At higher magnification, a SEM image of several martensite plates containing midribs. The residual taenite regions are structureless. 
(d) Optical image after etching of the same sulfide–metal intergrowth as in (c). The low Ni high Co metal, which is concentrated in the rim of the intergrowth, is overetched and appears black. The martensite plates and retained taenite regions around the sulfide intergrowth appear unaffected. However, the sulfide intergrowth appears to extend slightly further into the martensite plates than the adjacent taenite. 
(b) A decomposed martensite regions containing crystallographically oriented particles of taenite.
The meteorite cooled so rapidly at >0.01 °C/yr through 250 °C that cloudy taenite could not form (t1). It cooled to a temperature between -75 and -200°C so that 80% of the taenite was transformed to martensite. A second impact at t2 shocked the meteorite to <30 GPa and heated it to 320–400 °C for about a year causing martensite to decompose to kamacite and Ni-rich taenite. The third impact excavated Tishomingo as a meter-sized object around 100–200 Myr ago and exposed the object to cosmic rays.
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