Clunch is a type of stone that is mid-way in the transformation from chalk to limestone. It is a traditional building material in eastern England and Normandy.

Clunch is comparably soft and easy to quarry and work, but is more durable than chalk; it is used both in rubble masonry and in cut-stone masonry. It provides some of the older buildings on the English coast with distinctive white-stone walls, although these are usually protected by a layer of rendering.

It is easy to mine, usually from quarries -- often called chalk pits or clunch pits -- which are quite easy to excavate, as the clunch is usually found under a layer of easily excavated chalk, and mined downwards until the clunch becomes harder than is desired. It is usually still wet when quarried, and is easier to cut when wet; it is allowed to dry before use in construction.

Although it is tougher when dried, it is still prone to weathering and erosion, including frost damage, so it is most often coated in stucco, cement, or limewash. Historically, houses were often wattle and daub, with clunch used for foundations, chimneys, and other bits that benefited from being made of stone. However, as clunch is porous and will absorb water, these were in turn built on a base of some less porous material, such as brick, flint, or sarsen. Most existing clunch buildings are churches, although boundary walls and outbuildings made of clunch are also still around. When protected from the elements, clunch is excellent for carving, so exposed clunch is often seen inside churches.

Clunch formed during the Cretaceous period, approximately 145–66 million years ago. Not all clunch is created equal, with some beds having numerous small shell fossils, others having a greenish tint due to the presence of glauconite. Flint inclusions may also be present.

In common usage, clunch may be used to refer to any low-quality, amalgamate stone. Masons may refer to any workable chalk as clunch. Historically, clunch was used as an insult, and calling someone a clunch was equivalent to calling them weak or worthless.