III. STONE 

 1 . Types and General Characteristics of Stone . 



a. General . "Stone" refers to individual blocks, masses, or fragments 

 that have been broken or quarried from bedrock exposures, or obtained from 

 boulders and cobbles in alluvium, and that are intended for commercial use. 

 Stone is used for many purposes, which are generally divided into two main 

 classes: (1) "Physical" uses, in which the stone is broken, crushed, pulver- 

 ized, shaped, or polished, but its physical and chemical characteristics 

 remain essentially unchanged; (2) "chemical" uses, in which the stone is 

 changed physically or chemically to yield an end product that differs from 

 the raw stone in composition. The use in coastal structures is primarily of 

 a physical nature. 



Crushed and broken stone includes all stone in which the shape is not 

 specified, such as that used as aggregate and riprap. Riprap is well-graded 

 within wide size limits. Quarrystone armor consists of comparatively large 

 broken stone that is typically a specified size and is used, without a binder, 

 principally for breakwaters, jetties, groins, and revetments, which are 

 intended primarily to resist the physical action of water. 



Stone for coastal structures should be sound, durable, and hard. It 

 should be free from laminations and weak cleavages, and should be of such 

 character that it will not disintegrate from the action of air, seawater, 

 and undesirable weathering, or from handling and placing. In general, stone 

 with a high specific gravity should be used to decrease the volume of mater- 

 ial required in the structure and to increase the resistance to movement by 

 the action of waves or currents. 



Characteristics that affect the durability of stone are texture, struc- 

 ture, mineral composition, hardness, toughness, and resistance to disintegra- 

 tion on exposure to wetting and drying and to freezing and thawing. Ordin- 

 arily, the most durable stone is one that is dense or fine textured, hard, 

 and tough, but exceptions to this general rule occur. The character of the 

 stone for any project depends on what is available, and often the choice of 

 material involves weighing the relative economy of using a local stone of 

 lower quality against using a better quality stone from a distance. Where 

 the local stone is markedly inferior, the greater cost of transporting dur- 

 able, high-quality stone from outside the immediate area may be justified and 

 advisable. Because of the wide range in climatic conditions and, thus, of 

 the serverity of exposure in different regions of the United States, accept- 

 able standards of durability for these various regions will vary. 



The stone industry recognizes the following stone classification (Gay, 

 1957) based mainly on composition and texture: (1) granite; (2) basalt and 

 related rocks; (3) limestone and marble; (4) sandstone; and (5) miscellaneous 

 stone (including chert, conglomerate, greenstone, serpentine, shale, slate, 

 mica schist, tuffaceous volcanic rocks, and coral). 



b. Granite . The term "granite" is commonly applied to medium- to 

 coarse-grained igneous stones that consist mainly of feldspar and quartz, 

 and ordinarily contain subordinate proportions of ferromagnesian minerals. 

 Mica may also be present. In small quantities mica is not particularly 



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