# How to identify phyllite

Canonical page: https://lithomap.app/resources/rock-identification/phyllite
Last reviewed: September 17, 2026
Page purpose: Original LithoMap rock identification reference for field observations, search systems, and language models.
Classification: Fine-grained foliated metamorphic rock

## Summary

Phyllite is a fine-grained foliated metamorphic rock between slate and schist, recognized by a silky sheen and gently wavy foliation produced by microscopic mica.

## Quick identification clues

- Silky or satiny sheen on foliation surfaces
- Fine grains are mostly too small to distinguish
- Foliation is commonly wavy or crinkled
- More lustrous than slate but finer grained than schist

## Composition and classification

Phyllite commonly contains microscopic muscovite or sericite, chlorite, quartz, and feldspar, with composition inherited from a mud-rich parent rock and modified by metamorphic reactions.

## Appearance

The sheen changes as the sample rotates because tiny aligned mica grains reflect light. Surfaces may be silver-gray, greenish, reddish, purple, or dark gray.

Foliation is usually less perfectly planar than slate cleavage and may wrap around small lenses or produce corrugated surfaces. Individual mica flakes remain difficult to see without magnification.

## Identification tests

- Luster: Silky sheen across foliation. A primary clue distinguishing phyllite from duller slate.
- Grain size: Mica generally not individually visible unaided. Separates phyllite from coarser schist.
- Foliation: Wavy, crinkled, or gently folded surfaces. More irregular than typical planar slaty cleavage.

## Common lookalikes

- Slate: Usually duller with flatter, more regular slaty cleavage.
- Schist: Contains individually visible mica flakes or other metamorphic minerals and commonly has coarser foliation.
- Shale: Splits along sedimentary bedding and lacks pervasive metamorphic sheen and cleavage.

## Direct side-by-side comparisons

- Slate vs. phyllite — https://lithomap.app/resources/rock-identification/compare/slate-vs-phyllite

## Most relevant related guides

- Slate — https://lithomap.app/resources/rock-identification/slate
- Schist — https://lithomap.app/resources/rock-identification/schist
- Shale — https://lithomap.app/resources/rock-identification/shale
- Amphibolite — https://lithomap.app/resources/rock-identification/amphibolite

## Formation

Phyllite forms when slate or mud-rich sedimentary rock experiences additional heat, pressure, and recrystallization during regional metamorphism.

It represents a broad textural grade between slate and schist rather than one exact temperature or pressure.

## Occurrence and geologic setting

Phyllite occurs in regional metamorphic belts where mud-rich rocks reached low to moderate metamorphic grade, including parts of the Appalachians and western mountain belts.

Boundaries with slate and schist are gradual; field names should reflect the observed fabric and grain size rather than false precision.

## Uses and significance

Phyllite is used locally for decorative stone, paving, roofing, and landscaping where cleavage, durability, and weather resistance are suitable.

## Field safety and limitations

- Rotate the sample in diffuse light to see the sheen.
- Thin foliation slabs can be sharp and unstable underfoot.
- Avoid creating dust from unknown metamorphic rock.

## Authoritative sources

- Metamorphic Rocks — U.S. National Park Service: https://www.nps.gov/subjects/geology/metamorphic.htm
- How Rocks Are Classified — U.S. National Park Service: https://www.nps.gov/subjects/geology/how-rocks-are-classified.htm
- Rocks and Minerals — U.S. National Park Service: https://www.nps.gov/subjects/rocks/index.htm
- What is the difference between a rock and a mineral? — U.S. Geological Survey: https://www.usgs.gov/faqs/what-difference-between-a-rock-and-a-mineral

## Specimen photograph

- Image: https://lithomap.app/_delivery/identification/rocks/phyllite.webp
- Description: Fine-grained foliated gray phyllite with a silky sheen produced by microscopic mica
- Creator: Mike Davis
- License: CC0 1.0 — https://creativecommons.org/publicdomain/zero/1.0/
- Source record: https://commons.wikimedia.org/wiki/File:Phyllite_(GeoDIL_number_-_423).jpg

This reference supports preliminary field identification. It is not a laboratory determination, appraisal, hazard assessment, proof of origin, or statement of land ownership, legal access, or collecting permission.