Feldspar in Pennsylvania
Ralph W. Stone and H. Herbert Hughes
Pennsylvania Geological Survey Bulletin M 13, 1931

Cover letter

The feldspar industry is one of the smaller industries of the State.  During the first twenty years of this century the production of feldspar in this State amounted to 265,000 tons valued at $1,990,000.  Twenty years ago Pennsylvania ranked second among the States for crude feldspar production; ten years ago her production was sixth in quantity and fourth in value; in 1928 (the latest year for which figures are available at this time) Pennsylvania held eighth place with an output of only 2052 tons.

Uses


Feldspar is a mineral produced in the United States largely in Maine, New Hampshire, New York, and North Carolina and used in the manufacture of pottery, enamel ware, enamel brick and electrical porcelain.  Pennsylvania is a small producer.  The consumption in the United States is divided as follows:

In the ceramic industry the great use is as a constituent part of both body and glaze in true porcelains, white ware, and vitrified sanitary ware, and as a constituent of the slip (under glaze) and glaze in the so-called porcelain sanitary ware and enamel brick.  In the body of vitrified wares feldspar ranges from 10 to 35 per cent.  It serves as a flux to bind the particles of clay and quartz together.  Glazes contain a higher percentage, 30 to 50 per cent, of feldspar.

For use in pottery it is required that feldspar be nearly free from any mineral that will not burn white; especially it must be free from iron-bearing materials (biotite, hornblende, tourmaline, garnet etc.).

Enamels applied to metals are fused with feldspar.  Our modern gleaming white bathtubs and wash bowls are usually made of cast iron to which while still hot is applied an enamel containing much feldspar.  It may enter ingot he manufacture of plate, window, and bottle glass as a source of alumina and of the alkalies, and with fluorspar is commonly used in opalescent glass.

Small quantities of the purest grade of potash feldspar are used in the manufacture of artificial teeth.  Several operators in Pennsylvania in former years have selected the best lumps or large crystals of microcline for this market.  Dental spar, as the quarry men call it, used to bring the highest price, $6 to $8 a barrel of 350 pounds.

In some Portland cement plants where dust is collected to recover potash, the yield of potash is increased by the use of potash feldspar in the batch.

Crushed spar is used in considerable quantity in the form of granules on roofing material and also in the facing of cement blocks, particularly on those design dot resemble granite.  For this purpose the feldspar of course need not be high grade; in fact pegmatite from which the spar cannot be separated economically may be used for this purpose.  Poultry grit is another use and outlet for low grade spar.  It need only be crushed and screened to the size suitable to be attractive to poultry, one size for mature or large fowls and a smaller size for chicks.

Scouring soaps and abrasives made of feldspar differ from those made of quartz and other minerals in the degree of hardness of the individual grains.  Feldspar is slightly softer than glass and so less liable to scratch windows or glassware than soaps in which quartz or other harder material is the abrasive substance.

A small quantity of feldspar is used annually used for making carborundum, emery, and other abrasive wheels.  The feldspar fuses and on cooling binds the abrasive grains together.