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A group of dark-colored basic intrusive igneous rocks composed chiefly of labradorite or bytownite and augite. It is the approximate intrusive equivalent of basalt.

Gallet (British)

A stone chip or spall.

Gang Saw

A mechanical device employing a series of parallel reciprocating saw blades to cut stone blocks into slabs of predetermined thickness. The most common variety of gang saw used in the stone industry uses a slurry containing steel shot as the abrasive medium; but diamond segments mounted to steel blades are commonly used in gang sawing softer stone such as marble or limeston


Any process, although most frequently grinding, done to reduce the effects of the tolerances of stone slab thickness. Gauging may be done to a precise thickness with a specific tolerance, or may simply be done to two or more stones until the thickness of the lot is uniform. See also calibrate.

Glass Seam

A trade term in the limestone industry for a former fracture or parting that has been naturally recemented and annealed by deposition of transparent calcite. Similar to calcite streak, but transparent. Compare with dry seam.

Gloss Meter

An instrument designed to measure the reflectivity of a surface.


Coarse-grained, metamorphic rock with discontinuous foliation caused by planar alignment of plate and lath-shaped minerals. When used for building stone, generally classed as trade granite. Most gneiss is dark and composed mainly of quartz, feldspar, mica and ferromagnesian mineral (iron-magnesium silicates).


1. A quarry term for a plane of parting in a metamorphic rock, e.g. slate; the direction along which a stone is more easily broken, split, or cut. The main direction of the mineral composition and arrangement in stone.
2. A very small (less than a few millimeters diameter) particle of rock, such as a sand grain.
3. A general or descriptive term used to describe the relative size of crystalline rock components, as in “fine-grained” and “course-grained.”


A very hard, crystalline, igneous rock, gray to pink in color, composed of feldspar, quartz, and lesser amounts of dark ferromagnesium materials. Gneiss and black “granites” are similar to true granites in structure and texture, but are composed of different minerals. Commercial and scientific definitions of the granite group are explained in detail in ASTM C119.

Granite (commercial definition)

A term that includes granite (as defined below) plus 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 larvikite.

Granite (scientific definition)

A visibly granular, crystalline rock of predominantly interlocking texture composed essentially of alkalic feldspars and quartz. 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.



Stones having a texture characterized by particles that are apparent to the unaided eye. For sedimentary rocks, particles less than 4 inches in diameter and approximately equal in size.



A metamorphic rock, typically with poorly defined granularity, ranging in color from medium-green or yellowish-green to black. Refer to greenstone group in ASTM C119.


To remove portions of stone material by any abrasive method. Grinding may be part of producing a finish, shaping a profile, achieving a specific dimension, creating flatness between adjacently installed pieces, or part of a restorative effort.


1. A mixture of cementitious material and water, with or without aggregate, proportioned to produce a plastic consistency without segregation of the constituents; also a mixture of other composition but of similar consistency.
2. To place and tool grout in the joints of stonework.
3. In quarrying: a term describing the product of the quarry which is unusable for dimension stone, often piled near the extraction site.



A device used for cutting stone slabs to sizes by means of wedges driven by hydraulic pressure. The resultant fracture is of low precision, with a ragged, chipped appearance.