|
Glossary Of Natural Stone Trade Terminologies - G
Author:bea Date:2009-2-19 Read:34
Gangsawed – 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 – descriptions of 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 structurally sound.
Grade course – beginning course at the grade level, generally waterproofed with a damp check or damp course.
Grain – the easiest cleavage direction in a stone. "With the grain" same as "natural bed." Also, particles (crystals, sand grains, etc.) of 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 included 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 mineralogic compositions and the corresponding varieties of porphyritic textures. The term commercial granite shall also include other feldspatic 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, gneiss is characterised by relatively thick layers as compared with 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 of slabs, they are valued specifically for their dark gray to black colour when polished. Scientifically, they are far removed in composition form true granites though they may be satisfactorily used for some of the purposes to which commercial granite are adapted. They possess as interlocking crystalline texture, but unlike granite, they contain little or no quartz or alkalic feldspar, and are characterised by an abundance of one or more of the common black rock-forming minerals (chiefly pyroxenes, hornblende, and biotite).
Granular – having a texture characterised by particles that are apparent to the unaided eye. For sedimentary rocks: particles less than 4 inches (10mm) in diameter and approximately in size.
Greenstone – includes stone that have been metamorphosed or otherwise changed so that they have assumed a distinctive greenish colour owing to the presence of one or more of the following minerals: chlorite, epidote, or actinolite.
Greenstone is an old field term applied to metamorphosed igneous rock of mafic or ultramafic (low silica) composition (i.e., basalt, diabase, gabbro, peridotite and serpentinite).
Greenstone derived from basalt and other dark volcanic rocks consists dominantly of epidote, actinolite and plagioclase. No present commercial production such rock is known. Peridotite consists dominantly of olivine and pyroxene.
Serpentine consist largely of talc, chlorite, and serpentine; further alteration may result in soapstone.
Grout – mortar of pouring consistency. Coarse grout, used for wide grout spaces 2 inches (5cm) or more, consist of one part Portland cement, not more than two to three parts sand, and not more than two parts pea gravel. Fine grout, used in narrow grout spaces; consist of one part Portland cement and two-and-one quarter to three parts sand.
|
