Feldspar is the name applied to a group of minerals that are mainly
silicates of potassium, sodium, and calcium. Various kinds of feldspar
are used industrially in making glass, enamels, pottery, and other
products. All the feldspar now used in Illinois is shipped into the
state. The discovery by the Illinois Survey that some Illinois sands
contain considerable feldspar led Survey geologists and chemists to find
where deposits highest in feldspar occur, what kinds of feldspar they
contain, and whether it could be separated from the sand in which it
occurs. Beach sands, river sands, dune sands, and sands from other kinds
of deposits were studied.
It was found that many sands contain more than 15 percent feldspar and
some as much as 25 percent. Means of separating the feldspar from the
sand are believed to exist, but problems relating to the purity of the
separated spar remain to be solved.