Which metamorphic texture indicates formation under uniform stress, as opposed to directed pressure?

• A. Slaty
• B. Phyllitic
• C. Granoblastic
• D. Schistose

Answer: (D)

Uniform (or nondirectional) pressure produces a granoblastic texture, where minerals recrystallize without forming a preferred orientation. The result is a non-foliated, interlocking mosaic of grains, typical of rocks formed under heating with uniform stress, such as those from contact metamorphism (think marble or quartzite).

In contrast, when pressure is directed, minerals align into layers or bands, creating foliated textures. Slaty texture shows very parallel cleavage at low grades, phyllitic texture has a sheen with some foliation at higher grades, and schistose texture features pronounced alignment of platy minerals like mica into detectable slaty to schistose foliation. Hence granoblastic is the texture indicating formation under uniform stress.