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Highly oxidized Ni-rich spinel crystals have been found throughout the world at the Cretaceous-Tertiary (K/T) boundary. Although these crystals are believed to derive from the K/T impactor, their formation conditions remain obscure. In this chapter, we present experimental results concerning the crystallization of oxidized Ni-rich spinel from melts of chondritic composition. The effects of varying oxygen fugacity, temperature, duration of the heat exposure, and cooling rate on the morphology, abundance, and composition of spinel have been studied for two types of chondrite, a CI-type carbonaceous chondrite (Orgueil) and an LL6-type ordinary chondrite (Saint Severin). This study supports the view that the spinel crystals reported worldwide at the K/T boundary are derived from meteoritic material that equilibrated at ƒ O 2 ≥ 10 -2 bar and T ≤ 1520°C. Such formation conditions rule out derivation of K/T spinel from known volcanic or impact processes. In particular, K/T spinel cannot be formed in terrestrial magmas that evolved under extremely low oxygen fugacities, near the fayalite-magnetite-quartz (FMQ) buffer. For the same reason, direct crystallization from impact melt rocks or direct condensation from the cloud of vaporized target and projectile material can be excluded. We propose that spinel crystals from the K/T boundary have crystallized in liquid ablation droplets produced during the interaction with the atmosphere of large meteoroids decelerated at low altitudes, under high oxygen fugacities. Our scenario implies multiple meteoroid impacts all over the Earth, resulting either from the fragmentation of the K/T impactor upon an oblique impact or from the encounter with a fragmented comet.

An accurate gas-phase acidity for germane (enthalpy scale, equivalent to the proton affinity of GeH3 (-)), ΔH acid (o)(GeH4) = 1502.0 ± 5.1 kJ mol(-1), is obtained by constructing a consistent acidity ladder between GeH4, and H2S by using Fourier transform-ion cyclotron resonance spectrometry, and 0 and 298.15 K values for the first bond dissociation energy of GeH4 are proposed: D0 (o)(H3Ge-H) = 352 ± 9 kJ mol(-1); D (o)(H3Ge-H) = 358 ± 9 kJ mol(-1), respectively. These results are compared with experimental and theoretical data reported in the literature. Methylgermane was found to be a weaker acid than germane by approximately 35 kJ mol(-1): ΔH acid (o) = 1536.6 kJ mol(-1).

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