Phyllite vs Schist: What Are They and What's The Difference?

This article compares and contrasts the materials phyllite and schist.

Phyllite vs Schist (Introduction)

If you’ve ever seen a piece of whole, unrefined mica, the ragged layers of mineral are easy to flake and break off.

You may also observe that some pieces of mica break a little easier than others, even though it’s the same type of mineral.

The main reason for the difference comes is the presence of phyllite or schist, two types of metamorphic rock sharing the same formation process. But phyllite is the precursor to schist. This means phyllite experiences less heat, chemical activity and pressure than schist. Ergo, schist is very brittle.

So, when you have a piece of shiny silvery mica that flakes with ease, it comprises schist.

But, if it’s a little darker with a mild sheen where you need an implement to break it apart, phyllite is present. However, both types of metamorphic rock can comprise other minerals, not just mica.

Metamorphic rocks come from alterations of existing rock that physically change it into something new.

This geological process, called metamorphism, involves increased heat temperatures, environmental pressure and chemical activity.

Metamorphism gradually recyrstallizes stones and it fundamentally changes their texture or mineral composition.

Phyllite and schist are some of the most common and come from sedimentary rock found near waterbeds like oceans, lakes and rivers.

What Is Phyllite?

Low levels of chemical activity, heat and pressure contribute to creating phyllite, a foliated metamorphic rock.

It comprises mica minerals sitting in a parallel alignment and appears flake-shaped.

This allows the rock to split easily into slabs or sheets. It has a shiny reflective sheen, which distinguishes it from slate.

They’re usually on the continental side of convergent plate boundaries.

Slate is the precursor to phyllite in the metamorphic process and forms when directed pressure buries sedimentary rock, which experiences mild levels of heat.

Phyllite is often greenish, black or gray but weathers down to a brown or tan color.

It’s fantastic sheen gives it a silvery yet nonmetallic aesthetic.

What Is Schist?

A foliated metamorphic rock, schist comprises flat grains of mineral that are quite large.

They often form on the continental side of a convergent plate boundary.

This is where sedimentary rocks, like mudstones and shales, experience massive force, compression, chemical alteration and heat.

This environment lends itself to transforming sediment into minerals like biotite, muscovite, chlorite and mica.

For a rock to form as schist, mudstone or shale begins as slate, then into phyllite, which finally results in the appearance of schist.

This can metamorphose even more into granular rock called gneiss. This means schist doesn’t require a specific mineral make up to classify as such. Therefore, even graphite, talc or hornblende from basaltic or carbonaceous sources can be schists.

How Are Phyllite and Schist Similar?

Both phyllite and schist are metamorphic rocks part of the same formation process.

In fact, phyllite is a precursor before turning into schist.

Either stone is all over the world, mostly near the continental side of convergent plate boundaries where shale and mudstone are common.

Because there are no minerals specific to the formation of either phyllite or schist, they can comprise anything.

However, some of the more common and frequent ones are mica, quartz, biotite or graphtie.

It’s the exposure to things like chemical activity, pressure and heat that classify a rock as either phyllite or schist.

This process results in a vertical mineral grain on the surface of the stone, which give both rocks the appearance of visible and distinct foliation.

This texture is what makes them breakable along the mineral grain direction.

How Are Phyllite and Schist Different?

Phyllite and schist are different in a variety of ways although they both are part of the same formation process for this metamorphic rock.

First, phyllite is the precursor to schist, which means it doesn’t have the same glittery sheen that schist does.

It’s often a very basic gray, black or greenish hue with a muted sheen.

Because phyllite comes before schist, it doesn’t experience as much intensity as schist.

This makes it a little tougher to break.

The pressure, heat and chemical activity is what makes schist so fragile.

This type of breakage is what geologists term, “schistosity.”

Why Do People Confuse Phyllite with Schist?

Because phyllite and schist often comprise mica as a main mineral in their composition, it’s easy for people to confuse them.

Mica is a highly shiny and glittery mineral that’s often silver or a nonmetallic dark gun metal color.

The other mineral that helps confuse things is the presence of quartz.

This presents a similar issue as mica.

There will be a sheen to the texture of the rock which may give phyllite the appearance of being schist.

The best way to be able to distinguish between the two when mica or quartz are present is by seeing how breakable it is in your hands.

If you require a tool to flake off the minerals, it’s likely phyllite.

But, if it practically crumbles in your hands, then it’s probably schist.

For What Purposes Are Phyllite and Schist Used?

Both phyllite and schist have many practical uses.

Phyllite makes for great decorative elements in landscaping and property adornment.

For instance, many people will surface garden paths out of it or use tiles comprising phyllite on kitchen floors as cladding.

Schist with mica has a wide variety uses in the cosmetics industry.

Because of how easily it pounds into a fine powder, it makes a perfect ingredient in eye shadow, lipstick, mascara, eyeliner, blush and lip-gloss.

It blends well, is very comedogenic and entirely safe to use on skin, even near the sensitive eye area.

Final Thoughts

Phyllite and schist are two of some of the most abundant metamorphic rocks you can find on earth.

They are fragile, with the capacity to break or flake apart due to the vast amounts of pressure they experience during metamorphism.

However, schist has a far more intense exposure and is therefore easier to break than phyllite.