Rock and Stone
Igneous or magmatic rocks are primarily crystallized from a fiery fluid silicate melt, either deep below the earth’s surface or at the surface. Texture and fabric of these rocks depend on their environment during crystalliLation. Granite, gabbro, basalt, porphyry, and others belong to this group.
Sedimentary rocks, or layered rocks, are formed by the concentration of debris of variable size and shape deposited by mechanical means or by precipitation, or by accumulation of organic skeletons and shells. Conglomerate, sandstone, shale, limestone marble, dolomite, travertine, and onyx marble are common sedimentary rocks.
Metamorphic rocks are derived either from igneous or sedimentary rocks recrystallized by the effect of pressure and temperature. Important rocks of this group are gneiss, slate, marble and crystalline quartzite. Figure 73 of the chapter Decay of Stone sketches the environments of the three main rock groups.
KeywordsSedimentary Rock Metamorphic Rock Igneous Rock Bedding Plane Clastic Sediment
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