QUARRY MATERIALS OF NEW YORK 1 77 



positions ; they are not found in calcite particles of ordinary bedded 

 limestones. 



In the metamorphic change from limestone to marble, the bedded 

 structure as shown by the separation into parallel layers is usually 

 obliterated. Marble normally has a massive appearance and is so 

 coarsely jointed that blocks of almost any size may be quarried. 

 It also lacks any definite cleavage, a feature that is of great ad- 

 vantage in the working of the stone. 



Serpentine marbles include several types. Serpentine is a hy- 

 drated silicate of magnesia and iron, which has the same hard- 

 ness as calcite. The associations of the two minerals, therefore, 

 does not afifect the capacity of a marble to take a polish. Verde 

 antique is a serpentine irregularly veined with calcite. Another 

 type consists of crystalline limestone in which occur scattered grains 

 of serpentine of the size of peas, giving a white base speckled 

 with green. Serpentine also occurs unmixed with carbonates and 

 then exhibits oftentimes an attractive appearance by reason of 

 variations in color which ranges from light translucent green to 

 dark green and even black. Its origin is traceable usually to the 

 decomposition of such minerals as pyroxene, amphibole and olivine. 

 The larger bodies of serpentine are formed by the weathering of 

 igneous rocks in which those minerals predominate. 



MINERAL CONSTITUENTS OF MARBLE 



Marbles may have either calcite (CaCOg) or dolomite 

 (CaMgCoOg) as the principal ingredient, or they may contain a 

 mixture of the two in any proportions. A pure calcite marble 

 would have the same composition naturally as the mineral itself, 

 which consists of lime (CaO) 56 per cent and carbon dioxide 

 (CO2) 44 per cent. Theoretically, a dolomite marble should con- 

 tain lime (CaO) 30.4 per cent, magnesia (MgO) 21.7 per cent and 

 carbon dioxide (CO.,) 47.8 per cent. These percentages, however, 

 are never found in commercial marbles, owing to the invariable 

 presence of other ingredients. The highest grades of white statu- 

 ary marble, as represented by the best Italian and Greek examples, 

 carry, however, over 99 per cent calcium carbonate, and there are 

 American marbles nearly, if not quite, as pure. 



Between calcite limestones and the dolomites, every degree of 

 gradation is to be found, since the two minerals intergrow with each 

 other in any ratio ; such mixed phases are commonly designated 

 as magnesian marbles or limestones, as the case may be. There is 



