This document discusses the physicochemical behavior and geologic significance of minor crystalline solids and elements, specifically titanium and phosphorus. It notes that Ti4+ and P5+ associate with network-modifying cations like Mg and Fe, affecting melt composition, mineral-melt equilibria, and liquid lines of descent. Silicate melts can become enriched in TiO2 and P2O5, especially at low melt fractions. P5+ may be hosted in silicate minerals, reducing the need for phosphate minerals to account for phosphorus in the Earth and planets. Extreme enrichments of P2O5 up to 17% have been reported in olivine, pyroxene, and slags. Partitioning

1. Minor Crystalline Solids and Elements: Physicochemical Behavior and Geologic Significance

3. TiO 2 -enrichment in silicate melts

4. TiO 2 -enrichment in silicate melts

5. P 5+ , geochemical significance Less of a phosphate mineral may be needed to account for the bulk P 2 O 5 of Solid Earth & Planetary systems (e.g., mantle) as silicate minerals may host P 5+ In the absence or prior to saturation with a phosphate mineral, mafic silicate melts may become enriched in P 2 O 5 , especially in the geochemically important low melt fraction regime Interactions between P 5+ -hosting silicates and accessory phosphates may affect the stability of the latter P 5+ -bearing silicates as a source of phosphorus for microorganisms in nutrient-limited, sub-surface environments.

6. Reports of extreme enrichment in Olivine and Pyroxenes: 2-4 wt.% P 2 O 5 in olivine and pyroxene in Pallasites [Buseck & Clark 1984] and in reduced terrestrial basalts [Goodrich 1984] 17 wt.% P 2 O 5 in zoned olivine crystals from ancient slags [Kresten et al. 1998] P oorly characterized silico-phosphates in Angrites [Mittlefehldt 2002] Isostructural solid solutions of silicates and phosphates are not common; Si 4+ , P 5+ and Al 3+ have similar radii but also different EN The higher the degree of SiO 4 -polymerization, the lower the P 2 O 5 content, e.g., Gt > Ol >> Px ( Koritnig 1965; Henderson 1968; Anderson & Greenland 1969; Thompson 1975; Bishop et al. 1978; Brunet & Chazot 2001) EN=1.8 Phosphorus in silicate minerals Al 3+ 0.39 Å EN=1.5 P 5+ 0.31 Å EN=2.1 Si 4+ 0.26 Å

7. 5-9 GPa supersolidus experiments Sample in graphite capsule “ hard” Al 2 O 3 sleeve crushable Al 2 O 3 sample WC cubes Opx 9 GPa, 1775 °C Ol Gt

8. All JSC data for P 2 O 5 wt% in orthopyroxene [0.011(6) wt.%], olivine [0.07(3) wt%], and garnet [0.24(5) wt.%] in equilibrium with liquid [0.7-1.5 wt%]