Characteristics

Due to the flake-shaped mica's present this rock breaks easily into sheets or slabs. This rock type can be distinguished from slate by its reflective sheen. Phyllite originate from regional metamorphism at convergent plate boundaries involving continental lithosphere, which mean it forms under low pressure and low temperature conditions.

Composition

Phyllite contains tiny grains of mica minerals and all the minerals present are smaller than what can be seen with the naked eye. However sometimes there are other metamorphic minerals present as crystals and these can be seen by the unaided eye. These crystals are called porphyroblasts. Its reflective color owes it to the fact that organic material present in the parent rock is transformed into graphite.

References

• NEN-EN-ISO 14688-1:2019
• https://geology.com/