abacus

The flat slab on top of a capital.

abrasive hardness

The wearing quality of stone

acanthus

A plant with leaves on which the Corinthian and Composite capital are based.

acid rock

Igneous rock containing more than 66% silica.

alabaster

Fine-grained compact pale-coloured variety of gypsum.

alcove

A recess in a wall.

altar

A slab or table used for religious ceremonies.

Amberley

Chalk quarried in Sussex .

ambo

A lectern in early churches.

ammonite

Spiral fossil

angle-tooled

Dressed with diagonal tool marks.

antefixae

Small decorative blocks on a parapet.

apex stone

Top stone of a gable, spire or pediment.

apron

A panel below a window cill.

apse

The east end of a chancel or nave.

arcade

A range of arches on piers or columns.

architrave

(1) The lowest of three parts of an entablature

(2) The moulding round a door or window.

archivolt

An architrave moulding following the contours of an arch.

arenaceous

Composed of sandy grains

argillaceous

Containing clay minerals.

arris

External edge produced by the meeting of two planes.

artifical stone

Cast cementitious material containing crushed stone.

ashlar

Walling of plain blocks of stone.

astragal

A small moulding semi circular in section.

atrium

A covered inner courtyard.