Why can marble and quartzite remain non-foliated even if they are metamorphosed under directed pressure.

its something i have to know for the big test tomorrow and i cant seem to find the answer.

Marble is made of calcite crystals and quartzite is made of quartz crystals. In the metamorphic rocks, these crystals are "equant" meaning about the same size in different dimensions. They are somewhat blocky or ball like. As a result no alignment can be noticed, even if the rocks that contain them were under pressure.

Minerals like micas or tourmaline do have a long dimension and can indicate direction of pressure by lining themselves up. With these minerals, foliation is easily seen.

Consider a limestone layer and a shale layer both being exposed to metamorphic heat and pressure. The limestone undergoes metamorhism to slate, then phyllite and schist. All are foliated metamorphic rocks and the foliation is easily seen in the orientation of the mica. But the limestone layer, consisting just of calcite, has undergone the same temperatures and pressures but remains unfoliated. That is simply because there are no minerals in it that would show alignment. All of the grains look the same from different directions.

It is because they are made of only one mineral. When there are more minerals, the alignment is more obvious as the rock appears layered. Truth is, marble and quartzite can be foliated, but it is hard to detect. Foliation is more easily seen on a microscopic scale, rather than in hand specimen.