MetamorphicSoil pH usually 7.0–8.0

Marble

Limestone recrystallised — the fossils gone, and in acid country a narrow stripe of sweet ground that grows something different.

How it forms

Carbonate rock is caught in a mountain-building event and taken deep. It does not melt; the calcite simply recrystallises, each grain growing into its neighbours, until the whole mass is a single interlocking fabric that glitters in the sun.

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
Limestone or dolostone that has been buried, heated and squeezed until its grains dissolved and regrew as interlocking crystals of calcite. Everything that was in it — bedding, fossils, mud — is erased.
How to know it
Pale and sugary, with a visible sparkle from the calcite crystals on a fresh break. Fizzes in vinegar like the limestone it came from, but shows no bedding and no fossils at all.
How it wears
Dissolves like limestone but more evenly, rounding into smooth pale outcrops rather than the fissured pavements limestone makes.
What it means above ground
Pockets of sweet soil in otherwise acid country, and they show: a band of marble through granite or gneiss grows a visibly different flora — ferns, orchids and lime-loving wildflowers in a narrow stripe you can follow across a hillside.
Where you stand on it
The Grenville belt through the Gatineau Hills, eastern Ontario and the Adirondacks; Vermont and western Massachusetts; the Sierra Nevada foothills.
What lives on it
Maidenhair and walking fern, hepatica, yellow lady's slipper and other orchids — species that stop dead at the edge of the band.
What it's used for
Sculpture and cladding where it is clean, crushed for lime and terrazzo where it is not.
What it does to the soil
Sweetens the soil above it — raises pH, and grows a lime-loving flora.

Next to it in the cycle

  • Limestone

    what marble was before it was cooked

  • Gneiss

    the rock marble is usually found banded into

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.