Materials for porcelain, including flint, feldspar and kaolin, abound in the east portion of the Piedmont, the kaolin chiefly in Cecil county, and material for mineral paint in Anne Arundel and Prince George's counties, as well as farther north-west.
Feldspar, quartz and granite are quarried in the environs.
About 1896 some remarkably white and pure feldspar began to be quarried in Androscoggin, Oxford and Sagadahoc counties, but afterwards the spar mined in Maine was of less excellent quality; in 1907 the production in Maine was valued at $157,334, the total for the entire country being $499, 06 9.
Milford granite is the typical stone of an area reaching into Rhode Island south of the southern boundary of Providence county; it is a biotite granite of post-Cambrian age, is generally pinkish-gray in colour (owing to the large proportion of feldspar among its constituents), and is widely used for building purposes.
The quarries of granite near Long Island Sound, those of sandstone at Portland, and of feldspar at Branchville and South Glastonbury, however, have furnished building and paving materials for other states; the stone product of the state was valued at $1,386,540 in 1906.
The light flesh colour of the feldspar, and the blue of the quartz give it in some places a slight pinkish tint, and it is now much used as a building-stone under the name of ` pink granite.'
Granites with an unusually large proportion of soda-lime feldspar), of various grey shades, sometimes tinged with blue, pink or buff, and always marked with black mica; the finer varieties take a high polish and are used for monuments, and the coarser grades are used for construction, especially of railway bridges, and for paving and curbing.
In Chester county, also, is one of the most productive deposits of feldspar, second in importance only to those of Maine.
The south-western part of the country, a vast and almost level plain, is known as Dar Homr. A granitic sand with abundance of mica and feldspar forms the upper stratum throughout the greater part of Kordofan; but an admixture of clay, which is observable in the north, becomes strongly marked in the south, where there are also stretches of black vegetable mould.