Rocks: A Glossary

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ANDESITE - A fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene and biotite.

ARCH - A curved masonry construction spanning an opening and supported at its sides or ends. Usually made from cut stone voussoirs, (interlocking wedge-shaped blocks) that carries downward pressure out to side walls or lateral abutments.

AshlarASHLAR - Building stone that has been smooth cut, or dressed, into uniformly square or rectangular blocks.

BALUSTRADE - A complete railing system consisting of a top handrail supported on balusters, or vertical rails, which sometimes rests on a bottom rail.

BASALT - A dense textured (aphanitic) igneous rock of a lava flow or minor intrusion composed essentially of labradorite and pyroxene, often displaying a columnar structure. Basalt is relatively high in iron and magnesia minerals and relatively low in silica, generally dark gray to black, and feldspathic. A general term in contradistinction to felsite, a light-colored feldspathic and highly siliceous rock of similar texture and origin.

Belt CourseBELT COURSE - A continuous horizontal course of flat stones marking a division in the wall plane.

BluestoneBLUESTONE - A hard argillaceous metamorphic sandstone of characteristic blue, gray and buff colors quarried in the states of New York and Pennsylvania.

BROWNSTONE - A reddish-brown sandstone whose color results from a high amount of iron oxide as interstitial material, typically used as a building material.

BRUSHED FINISH - Textured surface obtained by brushing a stone with a coarse rotary-type wire brush.

Bull NoseBULL NOSE - Convex rounding of a stone member, such as a stair tread.

CladdingCLADDING - The lightweight outer skin of a building that neither carries any weight nor supports the building, but which protects it from weather elements.

CLASS 2 PERMEABLE BASE: Consists of 70% 3/4" gravel, 20% plaster sand and 10% pea gravel.

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.

COPING - A flat stone used as a cap on a freestanding wall, usually to protect the wall from weather.

CORTILE - The term for an internal courtyard, usually open to the air, surrounded by arcades to blur the distinction between interior and exterior.

COURSED VENEER - A wall treatment achieved by using stones of the same or approximately the same height. 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.

CurbingCURBING - Slabs and blocks of stone bordering streets, walks, etc.

Cutting StockCUTTING 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.

Exposed AggregateEXPOSED AGGREGATE - Phrase applied to the larger pieces of stone aggregate purposefully exposed for their color and texture in a cast slab.

FinesFINES - The powder, dust, silt-size, & sand-size material resulting from processing crushed rock.

FINISHES - Surface treatments. The surface of stones may be finished in a number of different ways. In general, smooth surfaces tend to emphasize color and veining, while rough finishes tend to subdue the veins and markings. Commonly available as:

  • Bush-hammered - A pounding action that develops a textured surface
  • Flamed - A rough finish that is developed through intense heat
  • Smooth - machine finished by saw, grinder or planer
  • Honed - dull sheen, without reflections
  • Polished - mirror gloss with sharp reflections, the smoothest finish available, resulting in a high luster (gloss) appearance
  • Machine Tooled - 4-cut, 6-cut, chiseled, axed, pointed, etc.
  • Chat Sawn - irregular and uneven markings
  • Split Face - concave-convex
  • Rock Face - convex
  • Thermal - planed surface with flame finish applied by mechanically controlled means to create surface coarseness
  • Brushed - obtained by brushing the stone with a coarse rotary-type wire brush

FlagstoneFLAGSTONE - Thin slabs of stone used for flagging or paving walks, driveways, patios, etc.; generally fine-grained sandstone, bluestone, quartzite or slate although other stones may be used.

GAUGED OR GAUGING - A grinding process that results in the uniform thickness of all pieces of material to be used together.

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

HAND CUT RANDOM RECTANGULAR ASHLAR - A pattern where all the stone is hand cut into squares and rectangles, and where all the joints are fairly consistent. Similar to sawed-bed ashlar in appearance.

HAND DRESSED (also known as ROCK FACED ASHLAR) - A finish given to both veneer stone and cutting stock, 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 arras and the intended rustic finish on the face.

HearthstoneHEARTH STONE - Originally the large single stone or stones used for the floor of a fireplace; now most commonly used to describe the stone in front of the fire chamber and in many cases extending on either or both sides of the front of the fire chamber.

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


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LimestoneLIMESTONE - A sedimentary rock composed primarily of calcite or dolomite. The varieties of limestone used as dimensional stone are usually well consolidated and exhibit a minimum of graining or bedding direction. Limestones that contain not more than five percent magnesium carbonate may be termed calcite limestone, as distinguished from those containing between five and forty percent magnesium carbonate, and from those that contain in excess of forty percent as the mineral dolomite. Recrystallized limestones and compact, dense, relatively pure microcrystalline varieties that are capable of taking a polish are known as marbles.

LintelLINTEL - A stone beam or horizontal member spanning the top of an opening, such as a doorway or window, and supporting the wall above it.

MarbleMARBLE - 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.

NATURAL CLEFT - This generally pertains to stone 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.

ONYX - A variety of quartz in crystalline calcium carbonate form. It is
characterized by a structure of parallel bands, each differing in color or in
the degree of translucency. Onyx is considered to be a marble because it
can take a polish.

PARQUETRY - A flat inlay of stone floors in closely fitted geometrical or other patterns, often including two or more colors or materials.

PORPHYRY - An igneous rock in which relatively large and conspicuous crystals (phenocrysts) are set in a matrix of finer crystals.

QuartziteQUARTZITE - A compact granular rock composed of quartz crystals, usually so firmly cemented as to make the mass homogeneous. The stone is generally quarried in stratified layers, the surfaces of which are unusually smooth. Its crushing and tensile strengths are extremely high. The color range is wide.

QuoinsQUOINS - Stones at the external corner or edge of a wall emphasized by size, projection, rustication, or by a different finish.

RIPRAP - Irregularly shaped stones used for facing bridge abutments and fills; stones thrown together without order to form a foundation or sustaining walls.

RISE - Refers to the heights of stone, generally in veneer; the vertical dimension between two successive steps.

ROCK (PITCH) FACE - Similar to split face, except that the face of the stone is inclined to a given line and plane, producing a bold appearance rather than the comparatively straight face obtained in split face; stones laid up in a masonry wall with natural faces as received from the quarry, or dressed to resemble natural stone.

SAND SAWN FINISH - Stone surface left as it comes from a gang saw; moderately smooth, granular surface varying with the texture and grade of stone.

SandstoneSANDSTONE - A sedimentary rock consisting usually of quartz cemented with silica, iron oxide or calcium carbonate. Sandstone is durable, has a very high crushing and tensile strength, and a wide range of colors and textures.

SAWED EDGE - A clean cut edge generally achieved by cutting with a diamond blade, gang saw or wire saw.

SAWED FACE - A finish obtained from the particular process employed to produce building stone. Varies in texture from smooth to rough and is coincident with the type of materials used in sawing; characterized as diamond sawn, sand sawn, chat sawn or shot sawn.

SillSILL - A flat stone used under windows, doors and other masonry openings.

SLAB - A lengthwise cut of a large quarry block of stone approximately 5'x 8' in size.

SlateSLATE - A very fine-grained metamorphic rock derived from sedimentary rock shale. Characterized by an excellent parallel cleavage entirely independent of original bedding, by which cleavage the rock may be split easily into relatively thin slabs.

SMOOTH FINISH - The surface texture produced by planer machines plus the removal of objectionable tool marks; also known as smooth planar finish or smooth machine finish.

Snapped EdgeSNAPPED EDGE, QUARRY CUT or BROKEN EDGE - Generally refers to a natural breaking of a stone either by hand or machine. The break should be at right angles to the top and bottom surface.

SOFFIT - The finished underside of a lintel, arch, or portico.

SPALL - A stone fragment that has split or broken off the face of a stone, either by the force of a blow or by weathering. Sizes may vary from chip size to one and two man stones. Spalls are primarily used for taking up large voids in rough rubble or mosaic patterns.

SPLIT FACE (SAWED BED) - Usually sawed on the stone bed and split by hand or machine so that the face of the stone exhibits the natural quarry texture.

TOLERANCE - Dimensional allowance made for the inability of men and machines to fabricate a product of exact dimensions.

TreadTREAD - A flat stone used as the top walking surface on a step.

Veneer StoneVENEER STONE - Any stone used as a decorative facing material which is not meant to be load bearing.