BUILDING STONES. 149 



Quartzytes.J 



howevei', may be due in some measure to the fact that in reducing a block 

 for a test to the required dimensions with a hammer and chisel, it is more 

 likely to be checked and weakened if coarsely crystalline, as this rock is, 

 than if it be fine-grained; and some of the tests may have been influenced 

 by such imperfection in the samples. Still, the greatest care possible was 

 taken to avoid any unfavorable results from such a cause. 



The gabbro of Rice's Point, Duluth, has been employed in a few build- 

 ings at Duluth, both as cut trimmings and for rough walls. It has also been 

 used for monuments and for bases, to which it is specially adapted, being 

 cut under the chisel and polished more easily than any of the crystalline 

 rocks that contain quai'tz. The same kind of rock at Taylor's Falls has been 

 but little employed for any purpose, though the rock there is favorably sit- 

 uated both for working and for transportation. 



The labradorite rock (No. 8) has a lavender-blue or bluish-gray color, 

 and is vitreous and subtranslucent in thin sheets. It does not have the 

 opalescence which distinguishes the labradorite from the typical locality 

 and from Lewis county, New York, but it has a compact, perfectly crys- 

 talline texture, with crystals as large as J or f inch across. In some of the 

 "greenstone" at Beaver Bay are perfect crystals over two inches in diameter, 

 distributed porphyritically in the mass, but this structure is very rare. This 

 beautiful rock, when suitably handled, will constitute a valuable material 

 for ornamental slabs and columns, and probably also for china ware. Titanic 

 acid, which sometimes is found in this rock, even in large quantities, is found 

 in nearly all porcelain clays,* at least in those of New Jersey, and suggests 

 not only the possible origin of the kaolinic clays used for earthen-ware, but 

 also the adaptability of the undecayed rock to the same uses. 



2. QUAETZYTES. 



The red quartzyte at Redstone, in Nicollet county, which also is seen in 

 Cottonwood, Watonwan, Rock and Pipestone counties, is sparingly used for 

 building stone at points contiguous; and one or two car-loads are known to 

 have been shipped to Minneapolis. It is the hardest stone in the state, or in 

 the United States, probably, that can be stated to have been used for purposes 

 of building. It consists almost wholly of quartz (84.52 per cent.), the red 



Report on the clay deposits of New Jersey. Cook, 1878, p. Z74. 



