We report about the shock-compression response of highly porous (55% and 65% dense) mixtures of 4Al+3SiO2 powders having shock-induced phase transitions and chemical reactions. Shock recovery experiments were performed using the CETR/Sawaoka plate-impact system (P=40 to 100 GPa) and the Sandia Momma Bear A Comp B fixture (P=22 to 45 GPa). The recovered compacts contained the high pressure stishovite phase, products of chemical reaction, as well as unreacted constituents. The reaction products formed included Al2O3, metallic Si (ambient and high pressure phases), SiAl intermetallic, and kyanite (Al2SiO5). The shock-induced chemical reaction in 4Al+3SiO2 powder mixtures, appears to have been accompanied (or assisted) by the formation of stishovite, a high pressure phase of quartz.