Phyllite

Article summary

of thin section of phyllite (in cross polarised light) showing phyllitic texture Phyllite ( ) is a type of foliated metamorphic rock formed from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation. It is primarily composed of quartz, sericite mica, and chlorite. Phyllite has fine-grained mica flakes, whereas slate has extremely fine mica flakes, and schist has large mica flakes, all mica flakes of which have achieved a preferred orientation. Among foliated metamorphic rocks, it represents a gradation in the degree of metamorphism between slate and schist. The minute crystals of graphite, sericite, or chlorite, or the translucent fine-grained white mica, impart a silky, sometimes golden sheen to the surfaces of cleavage, called "phyllitic luster". The word comes from the Greek phyllon, meaning "leaf". The protolith (or parent rock) for phyllite is shale or pelite; or slate, which in turn came from a shale protolith. Its constituent platy minerals are larger than those in slate but are not visible with the naked eye. Phyllites are said to have a texture called "phyllitic sheen", and are usually classified as having formed through low-grade metamorphic conditions through regional metamorphism metamorphic facies. Phyllite has good fissility (a tendency to split into sheets).…

Key claims

No claims recorded.

Discussion questions

1. Summarise the article in your own words. Which single claim would you verify first, and why?
2. Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
3. If two sources disagreed about one of these facts, what would you need in order to trust one over the other?

Bibliography

No sources recorded.