The quartz crystals were subjected to the same stress as the mica crystals, but because quartz grows in blocky shapes rather than elongated ones, the crystals could not be aligned in any one direction. The low-grade metamorphism occurring at these relatively low pressures and temperatures can turn mafic igneous rocks in ocean crust into greenstone (Figure 6.27), a non-foliated metamorphic rock. Most foliation develops when new minerals are forced to grow perpendicular to the direction of greatest stress. Geologic units in Harford county, Maryland - USGS However, compositional banding can be the result of nucleation processes which cause chemical and mineralogical differentiation into bands. Burial metamorphism occurs when sediments are buried deeply enough that the heat and pressure cause minerals to begin to recrystallize and new minerals to grow, but does not leave the rock with a foliated appearance. Generally, the acute intersection angle shows the direction of transport. Physical Geology, First University of Saskatchewan Edition by Karla Panchuk is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted. Chapter 6. In this treatment, we'll describe metamorphic rock that does not show visible alignment of materials as massive. The tendency of slate to break into flat pieces is called slaty cleavage. Composed of minerals that do not elongate or align during metamorphosis, nonfoliated metamorphic rocks tend to be simpler than foliated rocks. Essentials of Geology, 3rd Ed, Stephen Marshak. Slate exhibits slaty foliation, which is also called cleavage. A fine-grained rock that splits into wavy sheets. . Amphibolite is a non-foliated metamorphic rock that forms through recrystallization under conditions of high viscosity and directed pressure. Foliated metaconglomeraat wordt gemaakt onder dezelfde metamorfe omstandigheden die leisteen of phylliet produceren , maar waarbij het moedergesteente . If the original limestone was pure calcite, then the marble will likely be white (as in Figure 7.10), but if it had various impurities, such as clay, silica, or magnesium, the marble could be marbled in appearance. Metaconglomerate is a rock type which originated from conglomerate after undergoing metamorphism. The cement matrix of conglomerate is not as durable as the grains, and hence when broken, conglomerate breaks around the grains. The slatey cleavage typical of slate is due to the preferred orientation of microscopic phyllosilicate crystals.