Glossary of Stone Terms

Glossary of Stone Terms

A

• abrasive finish – a flat non-reflective surface finish for marble.

• abutment – a solid stone “springer” at the lowest point of an arch or vault.

• adhered – veneer secured and supported through adhesion to an approved bonding material applied over an approved backing.

• agate – a variegated variety of quartz showing colored bands or other markings (clouded, mosslike, etc.).

• anchors – types of stonework include those made of flat stock (strap, cramps, dovetails, dowel, strap and dowel, and two-way anchors) and round stock (rod cramp, rod anchor, eyebolt and dowel, flat-hood wall tie and dowel, dowel and wire toggle bolts).

• apex stone – uppermost stone in a gable, pediment, vault or dome.

• arch – a curved stone structure resting on supports at both extremities used to sustain weight, to bridge or roof an open space.

• architrave – the member of an entablature resting on the capitals of columns and supporting the frieze.

• argillite – a compact sedimentary rock composed mainly of clay and aluminum silicate minerals.

• arkose – a sandstone containing 10% or more clastic grains of feldspar. Also called arkosic sandstone, feldspathic sandstone.

• arris – a natural or applied line on the stone from which all leveling and plumbing is measured.

• ashlar – stones basically rectangular in shape and exhibiting the split face of the stone revealing striations that can be quite colorful.

B

• back arch – a concealed arch carrying the backing of a wall where the exterior facing is carried by a lintel.

• baluster – a miniature pillar or column supporting a rail, used in balustrades.

• balustrade – an ornamental fencing consisting of a series of balusters supporting a handrail or molding.

• banker – bench of timber or stone on which stone is shaped.

• basalt – a dense-textured (aphanitic), igneous rock relatively high in iron and magnesia minerals and relatively low in silica, generally dark grey to black, and feldspathic; a general term in contradistinction to felsite, a light-colored feldspathic and highly siliceous rock of similar texture and origin.

• bed – the top or bottom of a joint, natural bed; surface of stone parallel to its stratification. (1) In granites and marbles, a layer or sheet of the rock mass that is horizontal, commonly curved and lenticular as developed by fractures. Sometimes applied also to the surface of parting between sheets. (2) In stratified rocks the unit layer formed by semidentation; of variable thickness, and commonly tilted or distorted by subsequent deformation; generally develops a rock cleavage, parting, or jointing along the planes of stratification.

• belt course – a continuous horizontal course of flat stones placed in line marking a division in the wall plane.

• bevel – when the angle between two sides is greater or less than a right angle.

• bluestone – a dense, hard, fine-grained, commonly feldspathic sandstone or siltstone of medium to dark or bluish-gray color that splits readily along original bedding planes to form thin slabs. Bluestone is not a technical geologic term. It is considered to be a variety of flagstone, the thin relatively smooth-surfaced slabs being suitable for use as flagging. The term has been applied particularly to sandstones of Devonian age that are being or have been quarried in eastern New York and Pennsylvania and in western New Jersey, but similar stones that occur elsewhere may be included. It has also been applied in places to thinly layered gneisses and schists that can be split and used as flagging, but such stones are not properly embraced by this definition, although they may be marketed properly as flagstone.

• bond stone – used in varying percentages to anchor or bond the stone veneer to the backing material. Bond stones are generally cut to twice the bed thickness of the material being used. border stone – usually a flat stone used as an edging material. A border stone is generally used to retain the field of the terrace or platform.

• box – a tapered metal box wedged in the top of columns or other heavy stones for hoisting.

• broach – to drill or cut out material left between closely spaced drill holes; a mason’s sharp-pointed chisel for dressing stone; an inclined piece of masonry filling the triangular space between the base of an octagonal spire and the top of a square tower; a type of chisel used for working narrow surfaces.

• brownstone – a sandstone of characteristic brown or reddish-brown color that is due to a prominent amount of iron oxide, as interstitial material.

• brushed finish – obtained by brushing the stone with a coarse rotary-type wire brush.

• building stone, natural – rock material in its natural state of composition and aggregation as it exists in the quarry and is usable in construction as dimension building stone.

• bull nose – convex rounding of a stone member, such as a stair tread.

• buttering – placing mortar on stone with a trowel before setting into place.

C

• calcarenite – limestone composed predominantly of clastic sand-size grains of calcite, or rarely aragonite, usually as fragments of shells or other skeletal structures. Some calcarenites contain oolites (small, spherical grains of calcium carbonate that resemble roe) and may be termed oolite limestone. Calcareous sandstones, in which the calcium carbonate is present chiefly as bonding material, are not included in this category.

• calcite limestone – a limestone containing not more than 5% of magnesium carbonate.

• calcite streaks – description of a white or milky-like streak occurring in stone. It is a joint plane usually wider than a glass seam and has been re-cemented by deposition of calcite in the crack and is structurally sound.

• canopy – a sheltering roof, as over a niche or a doorway.

• capital – the culminating stone at the top of a column or pilaster, often richly carved.

• carve – shaping, by cutting a design to form the trade of a sculptor.

• caulking – making a marble joint tight or leak-proof by sealing with an elastic adhesive compound.

• cavity vent – a vent or opening in the joints between stones to provide even atmospheric pressure and humidity between the cavity and outside air; to prevent condensation and the migration of water into the structure.

• cement putty-cream-butter – a thick creamy mixture made with pure cement and water which is used to strengthen the bond between the stone and the setting bed.

• chamfer – to bevel the junction of an exterior angle.

• chat-sawn finish – a rough gangsaw finish produced by sawing with coarse chat.

• cladding – non-load-bearing thin stone slabs used for facing buildings.

• cleavage – the ability of a rock mass to break along natural surfaces; a surface of natural parting.

• cleavage plane – plane or planes along which a stone may likely break or delaminate.

• coating – a protective or decorative covering applied to the surface or impregnated into stone for such purposes as waterproofing, enhancing resistance to weathering, wear, and chemical action, or improving appearance of the stone.

• cobblestone – a natural rounded stone, large enough for use in paving; commonly used to describe paving blocks, usually granite, generally cut to rectangular shapes.

• commercial marble – a crystalline rock composed predominantly of one or more of the following materials: calcite dolomite or serpentine, and capable of taking a polish.

• composite – a construction unit in which stone that is to be exposed in the final use is permanently bonded or joined to other material, which may be stone manufactured material, that will be concealed.

• conglomerate – gravel that has been cemented together with silica, iron oxide or calcium carbonate.

• contraction joints – spaces where panels are joined and which expand as the panels contract.

• control joint – provided so that the movement of different parts of the structure due to shrinkage, expansion, temperature changes or other causes do not transfer loads across the joint.

• coping – a flat stone used as a cap on freestanding walls.

• coquina – a limestone composed predominantly of unaltered shells or fragments of shells loosely cemented by calcite. Coquina is generally very coarse-textured and has a high porosity. The term has been applied principally to a very porous shell rock of Eocence age that has been quarried in Florida.

• corbel plates – plates of non-ferrous metal fixed into a structure to support stone cladding at intervals and over openings in such a way as not to be visible.

• cornerstone – a stone forming a part of a corner or angle in a wall. Also a stone laid at the formal inauguration of the erection of a building, not necessarily at a corner, usually incorporating a date or inscription.

• cornice – a molded projecting stone at the top or an entablature.

• course – a horizontal range of stone units the length of the wall.

• coursed veneer – this is achieved by using stones of the same or approximately the same heights. Horizontal joints run the entire length of the veneered area. Vertical joints are constantly broken so that no two joints will be over one another.

• crack – a break, split, fracture, fissure, separation, cleavage, or elongated narrow opening, however caused, visible without magnification to the human eye and extending from the surface into the stone, that must extend through the grain or matrix.

• cross-bedding – the arrangement of laminations of strata transverse or oblique to the main planes of stratification.

• crowfoot (styolite) – description of a dark gray to black zigzag marking occurring in stone. Usually structurally sound.

• crystalline limestone – a limestone, either calcitic or dolomitic, composed of interlocking crystalline grains of the constituent minerals and of phaneritic texture; commonly used synonymously with marble and thus representing a recrystallized limestone; improperly applied to limestones that display some obviously crystalline grains in a fine-grained mass but which are not of interlocking texture and do not compose the entire mass. (NOTE: All limestones are microscopically, or in part megascopically, crystalline, the term is thus confusing but should be restricted to stones that are completely crystalline and of megascopic and interlocking texture and that may be classed as marbles).

• curbing – slabs and blocks of stone bordering streets, walks, etc.

• cut stone – this includes all stone cut or machined to give sizes, dimension or shape, and produced in accordance with working or shop drawings which have been developed from the architect’s structural drawings.

• cutting stock – a term used to describe slabs of varying size, finish, and thickness which are used in fabrication treads, risers, copings, borders, sills, stools, hearths, mantels, and other special purpose stones.

D

• dacite – a fine-grained, extrusive (volcanic) rock, intermediate in color and composition between basalt and rhyolite

• damp-proofing – one or more coatings of a compound that is impervious to water applied to a surface above grade.

• defect – those features which affect or have the potential of affecting the structural soundness of building stone, or may affect the durability of the building stone. Sometimes used for visual features such as xenoliths or veins.

• dentil – block projections on an entablature.

• dentil course – the lower part of the cornice with dentils. The cornice is jointed to allow machines production of the dentils.

• dentils – small, rectangular blocks under a classical cornice, resembling a row of teeth.

• dimensional stone – quarried stones, generally two feet or more square, of a specified thickness. Usually with one or more mechanically dressed surfaces.

• dolomitic limestone – a limestone rich in magnesium carbonate, frequently somewhat crystalline in character, found in ledge formations in a wide variety of color tones and textures. Generally speaking, its crushing and tensile strengths are greater than the oolitic limestones and its appearance shows greater variety in texture.

• dowel – a short piece of non-ferrous metal or slate fixed into a mortise or sinking in the joints of adjoining stones to prevent movement.

• dressed or hand-dressed – the cutting of rough chunks of stone by hand to create a square or rectangular shape. A stone which is sold as dressed stone generally refers to stone ready for installation. Sometimes called scabbling.

• drip – a recess cut beneath and slightly behind projecting stone to prevent water from running down the face of the wall below.

• dripstone – a projecting moulding over the heads of doorways, windows and archways to throw off the rain. Also known as a “hoodmould” and, when rectangular, as a “label”.

• dry – an open or unhealed joint plane not filled with calcite and not structurally sound.

• dry wall – a dry wall is a stone wall that is constructed one stone upon the other without the use of any mortar. Generally used for retaining walls.

• durability – the measure of the ability of natural stone to endure and to maintain its essential and distinctive characteristics of strength, resistance to decay, and appearance, with relation to a specific manner, purpose, and environment of use.

E

• efflorescence – a crystalline deposit appearing on stone surfaces typically caused by soluble salts carried through or onto the stone by moisture, which has sometimes been found to come from brick, tile, concrete blocks, cement, mortar, concrete, and similar materials in the wall or above.

• entablature – in classical architecture, the upper part of an order, comprising architrave, frieze, and cornice.

• entasis – the curve of the upper two-thirds of a column.

• expansion bolt – a socket that grips a drilled hole in stone by expanding as the bolt is screwed into it.

• expansion-contraction joint – a joint designed to allow the expansion and contraction of a wall due to temperature change. An expansion joint compresses as panels expand, a contraction joint expands as panels contract. exposed aggregate – phrase applied to the larger pieces of stone aggregate purposefully exposed for their color and texture in a cast slab.

F

• face – this refers to the exposed portion of stone. The word “face” can also be used when referring to the edge treatment on various cutting stock materials.

• fascia – a horizontal belt or vertical face; often used in combination with moldings.

• ferruginous – limestone or sandstone containing a high proportion of iron oxide.

• fieldstone – loose blocks separated from ledges by natural process and scattered through or upon the regolith (“soil”) cover; applied also to similar transported materials, such as glacial boulders and cobbles.

• filling – filling the natural voids and veins in a stone with material (cement, shellac, or synthetic resins and similar materials often mixed with stone fines).

• fines – the residue resulting from the normal fabrication and processing of stone.

• finish – the final appearance exposed stone slab surfaces are fabricated to meet.

• finished stone – building stone with one or more mechanically dressed surface(s).

• fireproof – relatively incombustible.

• fissure – A visible separation along the crystalline boundaries naturally occurring in the stone.

• flagstone – thin slabs of stone used for flagging or paving walks, driveways, patios, etc. It is generally fine-grained sandstone, bluestone, quartzite or slate, but thin slabs of other stones may be used.

• fleuri cut – cutting quarried marble or stone parallel to the natural bedding plane.

• flooring – stone used as an interior pedestrian wearing surface.

• foliated – the layered, banded structure of rock.

• fracture – a break in rock produced by mechanical failure. Fractures include faults and joints.

• freestone – a stone that may be cut freely in any direction without fracture or splitting.

• frieze – a belt course, sometimes decorated with sculpture relief, occurring just under a cornice.

G

• gang sawed – description of the granular surface of stone resulting from gangsawing alone.

• gauged or gauging – a grinding process to make all pieces of material to be used together the same thickness.

• glass seam – a narrow glass-like streak occurring in stone; a joint plane that has been re-cemented by deposition of translucent calcite in the crack and is structurally sound.

• grade course – beginning course at the grade level, generally waterproofed with a dampcheck or damp course.

• grain – the easiest cleavage direction in a stone. “With the grain” same as “natural bed”. Also, particles (crystals, etc.) of a rock.

• granite – a fine to coarse-grained, igneous rock formed by volcanic action consisting of quartz, feldspar, and mica, with accessory minerals. Granite-type rocks include those of similar texture and origin.

• granite (scientific definition) – a visibly granular, crystalline rock of predominantly interlocking texture, composed essentially of alkalic feldspars and quartz; this is true granite. Feldspar is generally present in excess of quartz, and accessory minerals (chiefly micas, hornblende, or more rarely pyroxene) are commonly present. The alkalic feldspars may be present (1) as individual mineral species, (2) as isomorphous or mechanical intergrowths with each other, or (3) as chemical intergrowths with the lime feldspar molecule, but 80 + 3% of the feldspar must be composed of the potash or soda feldspar molecules.

• granite (commercial/building use) – a term that includes granite (as defined above), gneiss, gneissic granite, granite gneiss, and the rock species known to petrologists as syenite, monzonite, and granodiorite, species intermediate between them, the gneissic varieties and gneisses of corresponding mineralogic compositions and the corresponding varieties of porphyritic textures. The term commercial granite shall also include other feldspathic crystalline rocks of similar textures, containing minor amounts of accessory minerals, used for special decorative purposes, and known to petrologists as anorthosite and laurvikite.

• granite gneiss – a foliated crystalline rock composed essentially of silicate minerals with interlocking and visibly granular texture, and in which the foliation is due primarily to alternating layers, regular or irregular, of contrasting mineralogic composition. In general a gneiss is characterized by relatively thick layers as compared with a schist. According to their mineralogic compositions, gneisses may correspond to other rocks of crystalline, visibly granular, interlocking texture, such as those included under the definition of commercial granite, and may then be known as granite gneiss if strongly foliated, or gneissic granite if weakly foliated.

• black granite – rock species known to petrologists as diabase, diorite, gabbro, and intermediate varieties are sometimes quarried as building stone, chiefly for ornamental use, and sold as “black granite”. As dimension blocks or slabs, they are valued for their dark grey to black color when polished. Scientifically, they are far removed in composition from true granites though they may be used for some of the purposes to which commercial granites, are adapted. They possess an interlocking crystalline texture, but unlike granites, they contain little or no quartz or alkalic feldspar, and are characterized by an abundance of one or more of the common black rock-forming minerals (chiefly pyroxenes, hornblende, and biotite).

• granular – having a texture characterized by particles that are apparent to the unaided eye. For sedimentary rocks; particles less than 4 inches (10 mm) in diameter and approximately equal in size.

• greenstone – includes stones that have been metamorphosed or otherwise changed so that they have assumed a distinctive greenish color owing to the presence of one or more of the following minerals: chlorite, epidote, or actinolite.

• grout – pourable cementitious material.

• coarse grout – used for wide grout spaces 2″ or more, consists of one part Portland cement, two-and-a-quarter to three parts sand, and one to two parts pea gravel.

• fine grout – used in narrow grout spaces, consists of one part Portland cement and two-and-a-quarter to three parts sand.

H

• hand-cut random rectangular ashlar – a pattern where all stone is hand cut into squares and rectangulars. Joints are fairly consistent. Similar to sawed-bed ashlar in appearance.

• hand or machine pitch-faced (rock-faced) ashlar – a finish given to both veneer stone and cutting stock. This is created by establishing a straight line back from the irregular face of the stone. Proper tools are then used to cut along the line, leaving a straight arris and the intended rustic finish on the face.

• head – the end of a stone which has been tooled to match the face of the stone. Heads are used at outside corners, windows, door jambs, or any place where the veneering will be visible from the side.

• hearth – that part of the floor of a fireplace of stone on which the fire is laid.

• hearth stone – originally the single large stone or stones used for the hearth, now most commonly used to describe the stone in front of the fire chamber and many times extending on either or both sides of the front of the fire chamber.

• holes – sinkages in the top beds of stone to engage Lewis pins for hoisting.

• honed finish – honed is a super fine smooth finish, though not as fine as a polished finish.

• hydrate – a mineral formed by the combination of water and some other elements or compounds.

• hydrothermal – of or relating to hot magnetic emanations that are rich in water.

• hydrous – containing chemically combined water.

I

• igneous – one of the three great classes of rock (igneous, sedimentary, and metamorphic), solidified from molten slate, as granite and lavas.

• incise – to cut inwardly or engrave, as in an inscription.

• inscription – lettering cut in stone.

J

• jack arch – one having horizontal or nearly horizontal upper and lower surfaces. Also called flat or straight arch.

• joint – the space between stone units, usually filled with mortar.

• jointing scheme – a detailed architectural drawing showing the dimensions, locations and configurations of stone units and joints on the structure.

• jumper – in ashlar patterns, a piece of stone of higher rise than adjacent stones which is used to end a horizontal mortar joint at the point where it is set.

K

keystone – the last wedge-shaped stone placed in the crown of an arch, regarded as binding the whole.

L

• lava – a general term applied to igneous rocks, such as basalt and rhyolite, that erupted from the earth by volcanic action.

• lead buttons – lead spacers in the solid horizontal joints to support the top stone until the mortar has set.

• lewis bolt – a tapered head wedged in a tapered recess in stone for hanging soffit stones.

• lewis holes – holes in cut stone for lifting and support during setting of cut stones and sometimes for permanent support. Holes are checked for the particular Lewis lifting device or hook to be used.

• limestone – a sedimentary rock composed of calcium carbonate; includes many varieties. (See oolitic limestone, dolomitic limestone, crystalline limestone). Limestones that contain not more than five per cent magnesium carbonate may be termed calcite limestone, as distinguished from those that contain between five and 40 per cent magnesium carbonate (magnesium or dolomitic limestone), and from those that contain in excess of 40 per cent as the mineral dolomite (dolostone, formerly known as the rock dolomite). Recrystallized limestones and compact, dense, relatively pure microcrystalline varieties that are capable of taking a polish are included in commercial marbles.

• liners – strengthening elements attached to the back of stone slabs, usually a structurally sound section of similar stone dowelled and epoxied into place.

• lintel – the block of stone spanning the top of an opening such as a doorway or window; sometimes called a head.

• lipping – usually refers to flagging materials; caused when two pieces of material to be joined together are slightly warped or twisted causing one or more edges to be higher or lower than the adjoining material.

• lug sill – a stone sill set into the jambs on each side of masonry openings.

M

• machine finish – the generally recognized standard machine finish produced by the planers.

• malpais – literally, badland; refers to dark colored rock, commonly lava, in rough terrain. As defined for architectural use; calcium carbonate with other components which give it color, markings, and texture suitable as a desirable building stone.

• marble – a metamorphic limestone in a more or less crystalline state capable of taking a high polish. Occurs in a wide range of colors and variations. Marble that contains less than five percent magnesium carbonate may be termed calcite marble; from 5 to 40 percent magnesium carbonate, magnesian or dolomitic marble; and more than 40 percent dolomite marble. These limiting values are, however, not strictly established in petrologic science and are used herein as arbitrary limits.

• onyx – so called in trade, is a crystalline form, commonly microcrystalline, of calcium carbonate deposited usually from cold water solutions. It is generally translucent and shows a characteristic layering. Onyx marble is technically a misnomer, as true onyx is a variety of cryptocrystalline fibrous silica (chalcedony), and is closely related in form and origin to agate.

• serpetine – marble characterized by a prominent amount of the mineral serpentine.

• travertine – a form of limestone precipitated from ground waters, as in caves or in orifices of springs (see limestone group).

• verde antique – a commercial marble composed chiefly of massive serpentine and capable of taking a high degree of polish. Verde antique is not a true marble in the scientific sense, but is commonly sold as a decorative commercial marble and requires the adjectival modifier verde (or verd) antique. Verde antique is commonly veined with carbonate minerals, chiefly calcite and dolomite.

• masonry – built up construction, usually of a combination of materials set in mortar.

• metamorphism – the change or alteration in a rock caused by exterior agencies, such as deep-seated heat and pressure, or intrusion of rock materials.

• miter – the junction of two units at an angle of which the junction lines usually bisect on a 45 degree angle.

• modular multiple-cut (pattern-cut) – this refers to standard patterns used throughout the stone industry. These patterns are usually based on multiples of a given height. Stone that is multiple cut or pattern cut is pre-cut to allow typically for ¼″ or ½″ (6 or 13 mm) joints or beds.

• moldings – decorative stone deviating from a plane surface by projections, curved profiles, recessed or any combination thereof.

• mortar – a plastic mixture of cement, lime, sand, and water used to bond masonry units.

• mosaic – a veneering which is generally irregular with no definite pattern. Nearly all the stone used in a mosaic pattern is irregular in shape.

N

• natural bed – the setting of the stone on the same plane as it was formed in the ground. This generally applies to all stratified materials.

• natural cleft – this generally pertains to stones which are formed in layers in the ground. When such stones are cleaved or separated along a natural seam the remaining surface is referred to as a natural cleft surface.

• nicked bit finish – obtained by planing the stone with a planer tool in which irregular nicks have been made in the cutting edge.

• non-staining mortar – mortar composed of materials which individually or collectively do not contain material that will stain, usually ha