High-temperature condensates in chondrites and the environment in which they formed

Chemical compositions of melilitee and titaniferous pyroxenes in calcium- and aluminum-rich inclusions in carbonaceous chondrites are consistent with their origin as hightemperature condensates from a gas of solar composition. Thermodynamic calculations indicate that the highest temperature minerals equilibrated with the gas at temperatures in excess of 1400°K. The lack of evidence for direct condensation of gas to liquid enables us to set an upper limit to the pressure when the inclusions formed which may be as low as 2.2 × 10^?3atm. Glasses, which are commonly found in chondrules, are interpreted as quench products of liquids formed by secondary reheating of primary solid condensates. The high-temperature inclusions constitute evidence that accretion of grains to cm-sized objects occurred at a very early stage in the evolution of the solar nebula.