Phyllite or “leaf stone”, is a metamorphic rock made of mostly fine grained mica. Phyllite’s protolyth, or parent rock,is shale. Millions of years ago, shale was exposed to the heat of magma (up to 800 degrees Celsius) and to the pressure of millions of other rocks atop the shale. It metamorphosed into phyllite and was uplifted to the crust of the Earth. While all rocks are old, phyllite is an ancient rock.
Shale is a sedimentary rock made of mud that has flakes of clay minerals and quartz and calcite minerals. Through the process of metamorphism, shale becomes slate. Slate metamorphoses into phyllite.
Phyllite is a medium gray or greenish stone with a corrugated cleavage.It has sheen on its surface due to tiny plates of micas. The micas are biotite and muscovite which reflect a satiny luster. The mica crystals are just big enough to be seen by the naked eye. Muscovite, in particular, is very glittery. Phyllite can appear silver in sunlight.
Phyllites often form on the edges of regional metamorphic plates where clay-rich marine sedimentary rock, was caught between colliding continental plates. Phyllites may also form in sedimentary basins where marine muds have been buried extremely deep. Slate also comes from shale; phyllite is different from slate because it has metamorphosed more. While slate has straight lines and planes, phyllite is wavy. Phyllite has good fissility which means it has a tendency to split into sheets.
Rock landforms containing phyllite can be seen in Australia and New Zealand. These rock landforms originally lay far below sea level and are at their present location as a result of sedimentation, regional metamorphism, tectonic processes, weathering and erosion. Excavation by road building equipment also helped expose these rock landforms. Many mountain ranges, such as the Blue Ridge Mountains, are characterized by metamorphic rocks. Phyllite is found throughout North America and also in the Alps and the Scottish Highlands.
Phyllite can be used as countertops in homes. The Government Quarter in Oslo has phyllite floors designed in geometrical patterns. There are other prestigious buildings incorporating phyllite as architects and engineers have become more familiar with the properties of building with phyllite.
In conclusion, phyllite is an ancient metamorphic rock that comes from slate. Phyllite rock formations can be found in various regions of the world, including North America. In recent years, architects and engineers have begun using phyllite as an outstanding and beautiful building material.
