The general gradation with heat and/or pressure is mudstone/argillite to shale/pelite to slate to phyllite. With the heat and pressure comes an orientation of plately minerals (mica, chlorite ) as well as alteration to new minerals, like the formation of sericite and quartz. The sheen observed is from the platy mineral orientation which is usually too fine to see without magnification. The next stop in the increasing metamorphism is a schist.


Both shale and phyllite exhibit cleavage or foliation but in shale it is due to bedding (compaction and general orientation of detrital clay minerals) and in phyllite it is due to the oriented platy minerals from heat and pressure.

Also interesting are the inclusions (dark grey) in the phyllite in the bottom picture. Could they be siliceous nodules? This would indicate the possible sedimentary origin and parent rock of the phyllite.

ok. thanks you guys.