MetamorphicSoil pH 4.5–6.0, depending on the member

Metamorphic rock

Older rock changed in place by heat and pressure, deep in the crust, without ever melting.

How it forms

Burial, mountain building or the heat of a nearby intrusion pushes rock past the point where its minerals are stable. They break down and regrow as forms that are stable at the new conditions, usually lining up with whatever direction the pressure came from.

Metamorphic — changed by heat and pressure

Rock buried and squeezed from both sides, its minerals regrowing aligned across the direction of pressureheat and pressure, but never meltinggrains pointing every wayall in one plane

Rock taken deep, squeezed and heated until its minerals regrew in new forms, without ever melting. The new minerals line up under the pressure, which is why so many of these split in sheets or come out in stripes.

What it is
The family of rocks whose minerals regrew in the solid state. Some maps say only this much, which still tells you the rock will be hard, probably striped or sheeted, and will not hold fossils.
How to know it
Minerals aligned into sheets, stripes or a visible grain, with no bedding and no fossils. Generally harder than the rock it came from.
How it wears
Slowly, and along whatever grain the squeezing gave it.
What it means above ground
Generally thin, stony soil on hard ground, usually acid, with lakes wherever a hollow holds water.
Where you stand on it
The Canadian Shield, the Appalachians, and the cores of every western range.
What lives on it
Conifer and hardwood forest on thin soil, and acid-water lakes — unless a limey band runs through, in which case everything changes for its width.
What it's used for
Building stone, roofing, aggregate and abrasives.
What it does to the soil
Sours the soil above it — nothing in it neutralises rain, so the ground stays acid.

Next to it in the cycle

  • Gneiss

    the deepest-changed and most banded

  • Schist

    the glittering, sheet-splitting one

  • Marble

    the one that sweetens the soil instead of souring it

Is this what you're standing on?

Find the rock under your town

Enter a town or postal code and we'll show you the rock beneath it and how old it is, the soil it makes, and the chain of rivers your water joins on the way to the sea.

General descriptions of rock families. Any particular outcrop can differ — rocks grade into one another, and a geological map at this scale describes a district rather than a hillside.