Metamorphic rocks are a very outstanding process of a construction of a rock. Of course, they go through natural weathering events and components like every other rocks. But they start out as a rock and then slowly change into a whole different rock. It's all mostly thanks to heat and pressure. Because of this, metamorphic rocks has a very unique texture and patterns and new mineral structures.
Above is a picture of the Phantom Ranch which presents that the metamorphic rocks dominating this surface. The minerals in this picture did not crystalize from a magma but are steady at the high pressure and temperatures that are found deep in the crust.
The rocks were probably originally igneous or sedimentary rocks before 1.6 billion years ago. Then in time, the impact of the two tectonic plates pushed them deep under the crusts of the Earth. Then there, the rocks recrystallized without melting at high temperature and under massive pressure. The rocks then were folded and twisted and their textures
Most common metamorphic rocks found in Grand Canyons are schists, gneiss, quartzite, phyllite, slate, and marbles. They're not easily spotted as sedimentary rocks however you can see a few from here and there mixed.
The schists are formed from the sedimentary rock, shale. The shales are put under incredible pressure and heat causing a change of texture and structure of the minerals.
The gneiss is a metamorphism of an igneous rock, granites or diorites. It is formed when there is a lot of pressure and heat and when rocks melt. Gneiss are actually mostly used in buildings, roads, and curbs.
Quartzites are formed from sandstones. Sandstones goes in a high temperature and pressure from any sources, normally plate movements, and then have crystals recrystallize into larger connected crystals forming into one hard metamorphic rock; a quartzite.
Phyllite's rock parents are slates even though that is also a metamorphic rock that started out as a shale. Phyllite are just rocks that has been more metamorphosed than a slate. As a result, the straight lines that the slate breaks along but has a wavy appearance. If the phyllite is more metamorphosed, it will result to a schist.
A slate rock forms from shale which contained a lot of clay minerals. Then, those minerals gets put under pressure with temperature of at least hundred degrees or so which then converts to mica minerals. This process does two things first; the rock grows hard ro ring when a hammer hits it, and the rock gets a nice cleavage direction so that it breaks along flat planes.
A marble is a metamorphism of a sedimentary rock; usually a dolomite or a limestone rock. From the high temperature and pressure, the small crystals, from the limestone or dolomite, are fused to together that makes the marble. The swirls and line patterns on the marble might be a layer from the sedimentary rock.