The three Al-silicate polymorphs, kyanite, andalusite and sillimanite, are well-known geological markers used to determine the extent of P- and T-induced metamorphism experienced by rocks in the Earth's crust. Despite extensive study of their thermodynamic properties, there has only been one study (of kyanite published in 2016) as a function of pressure AND temperature. The compressibilities of andalusite and sillimanite have only ever been characterised at room temperature. In a recent HRPD study, I found that the latter two minerals exhibit negative linear thermal expansion below room temperature, which one would expect to translate into anomalous linear compressibility. In order to study this further I propose the first systematic PVT study of all three polymorphs using the Paris-Edinburgh press on PEARL.