MetamorphicSoil pH usually 4.0–5.0

Quartzite

Sandstone cooked until the grains fused into one mass. Nearly pure silica, and one of the hardest rocks there is.

How it forms

Quartz sandstone is heated and compressed. Quartz does not turn into anything else — there is nothing for it to become — so instead the grains simply weld, closing every pore until the rock is solid silica.

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
Metamorphosed sandstone in which the quartz grains have recrystallised into each other so completely that a break runs through the grains rather than around them.
How to know it
Glassy on a fresh break, and the break goes straight through the grains rather than around them, which is the test that separates it from sandstone. Usually white or pale pink, and it will scratch glass.
How it wears
Hardly at all. It resists everything, so it stands as ridges and white scree while the country around it wears down.
What it means above ground
Almost no soil, very sour, very poor. Barrens, stunted pine, lichen and bare white rock.
Where you stand on it
The Baraboo Hills of Wisconsin, the Uinta Mountains, the Sioux quartzite of Minnesota and South Dakota, and the ridges of the Appalachians.
What lives on it
Pitch pine, scrub oak, blueberry and lichen — a barrens flora adapted to almost nothing.
What it's used for
Railway ballast, abrasives, refractory silica brick, and durable decorative stone.
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

  • Sandstone

    what quartzite was before it fused

  • Marble

    the same process applied to limestone instead

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.