So sandstones make massive quartzites and limestones make marble, neither of which are strongly foliated. Here is an example of what marble looks like. Porphyroblasts are larger crystals in a finer-grained matrix. The metamorphic rock will bear the name of the dominant porphyroblasts, e.g. garnite schist. Mineral changes in metamorphic rocks Changing conditions results in phase transformation from one mineral to another.
Minerals coalesce or change crystal structure.
Therefore the presence of one particular form documents the PT conditions. A more accurate idea of PT conditions can be gotten by considering a whole suite of minerals. Determining the PT history of a sequence of rocks describes the journey of that particular crustal package up and down the tectonic elevator. Role of initial composition Obviously, the composition of the protolith plays a strong role in which minerals will grow. Thus basalts, granites and carbonate rocks each develope into the different metamorphic mineral assemblages leading ultimately to amphibolite, gneiss or marble respectively.