Shallowater is the only known unbrecciated, igneous aubrite (enstatite achondrite). It is a coarse-grained orthopyroxenite consisting of (in vol%) poikilitic orthoenstatite crystals (80) up to 4.5 cm in size which contain, as inclusions and in the interstices, xenoliths of an assemblage of twinned low-Ca clinoenstatite (1), forsterite (2.9), plagioclase (2.5), metallic Fe,Ni (3.3), troilite (2.9), schreibersite (0.4), weathered opaques (8), and traces of niningerite and oldhamite. Conclusions: 1. Shallowater is of igneous origin. 2. Shallowater could not have formed by internal, igneous, nor by impact melting processes, either on the H or L enstatite chondrite or aubrite parent bodies. Instead, Shallowater appears to be a sample of yet a fourth enstatite-type asteroid. 3. Shallowater experienced an extraordinarily complex and unusual, three-stage cooling history, as determined by mineral stability considerations and modelling of micro-structural evolution as a function of cooling rate. Stage 1: Very fast cooling from ≥1,580°C to somewhere above 712°C, at a rate of ≥100°C/hour through 1000°C; above 1000°C, the rate was probably much faster. Stage 2: Very slow cooling (annealing), from 712 to 680°C at a rate of ≤7.5°C/10 6 y. Stage 3: Fast cooling, from 680 to 600°C at a rate of ≥0.5°C/day and from 600 to 300°C at a rate of ≥0.4°C/day. 4. This complex cooling history suggests an equally unusual origin for Shallowater, as follows: A completely or partly molten asteroid of nearly pure enstatite composition was broken up by low-velocity impact with a solid, E-like object. The melt cooled very fast (stage 1), due to incorporation of cold (≥20%) projectile debris (the xenoliths). Fragments reassembled into a rubble-pile body while T was ≥712°C, and deeply buried materials (like the object that is now Shallowater) cooled very slowly from 712 to 680°C (stage 2). The anneal of stage 2 requires burial at a depth of 40 km on a 100 km diameter asteroid. Excavation from this depth by impact to account for the fast cooling of stage 3 can be accounted for in two scenarios. Scenario 1: During catastrophic impact, the Shallowater object could have been by chance near the surface (within 10 m) of a very large fragment, thus accounting for the fast cooling and for surviving for 4.5 × 10 9 y . Scenario 2: The Shallowater object may have been excavated by break-up and subsequently buried near the surface of a gravitationally reassembled body. This would require yet a second break-up and reassembly episode. 5. The xenoliths represent an enstatite-like meteorite type unknown as an individual fall, not unexpected for a rock type from an asteroid that appears to have been largely destroyed early in the history of the solar system.