The mining in the Cowee district is confined to mining for mica and no attempt is made to remove the feldspar except where it interferes with the mining of the mica. In the Sprucepine district, three feldspar quarries are now in operation and others are to be opened in the near future. The potash feldspars of North Carolina may be safely represented by the following analyses:

Analyses of potash feldspars of North Carolina.

Feldspar-bearing dikes have been found in various parts of Georgia, and the Geological Survey of Georgia has now under way an investigation of these deposits, but as yet no feldspar quarrying has been attempted in the State.

QUALITY OF THE PRODUCT.

The foregoing sets forth the general location and extent of the known feldspar deposits east of the Mississippi River.

In estimating the relative value of a feldspar and its adaptability to the various arts and industries due consideration must be given to the methods employed in the mining, refining, and pulverizing of the crude rock. For example, the feldspars of Maine are not naturally very pure; in fact, no feldspar produced in the United States has so many injurious associate minerals as that of Maine. Nevertheless, the Maine feldspars are furnished to the consumer in a state of purity second to none, except for the quartz content, which can not be eliminated and which must of necessity increase with continued mining in any district. This high state of purity is obtained only by untiring vigilance on the part of the miner and the mill operator to insure the removal of even the smallest particle of ironbearing impurity and, having freed the crude feldspar of all such impurity, to prevent any contamination during the milling process. The extra precautions necessary to insure such purity must of necessity increase the cost of the finished product. Not only must extra expense be incurred in handling and storing the crude feldspar

before it goes to the mill, but many labor-saving and highly efficient machines must be condemned because of their metal surfaces which come in contact with the sharp edges of the feldspar rock, and being ground off add an almost inappreciable content of iron to the finished product.

Inability to employ many modern machines and appliances has resulted in the general condemnation of the feldspar mining and grinding industry as unwilling to utilize modern appliances, but until machinery can be provided with all wearing faces made of material which will not contaminate the product the operator is to be commended rather than condemned for refusing to employ them.

A point which must be recognized by both the producer and the consumer of ground feldspar is the relation between the quality of the feldspar and the market price. The rejection of any proportion of the rock quarried requires that the accepted rock must be marketed at a price which will cover the expense of the entire quantity quarried unless the rejected material can be disposed of without loss in some other way. As the selection of the more choice parts continues, the amount of material handled continues to increase and this will ultimately result in increasing the cost of the finished product. It is therefore vitally important that every user of feldspar should have a proper understanding of the degree of purity which his business demands and, having done so, seek that grade of material where it can be obtained at the best advantage.

THE COLOR OF FELDSPARS.

The general opinion prevails that the small amounts of impurities which cause a natural feldspar to be cream, buff, brown, or salmon are lost in the fusing process, and that a dark feldspar may fuse to as perfect a white glass as a pure white feldspar. This is not true so far as the results of this investigation have indicated. The intensity of color in the fresh feldspar is, however, no indicator of the intensity of color in the fused feldspar nor of its coloring action in the pottery body or glaze.

In general the feldspars which fuse to the most colorless or white glasses are those which are pure white or colorless. The next in order are the pale salmon and nearly transparent feldspars; then come the cream feldspars, which are generally opaque, or nearly so; the next are the brown and buff feldspars; and the last and most highly colored when fused are the sea-green or olive-green brown feldspars.

This classification is for feldspars which do not contain any foreign material other than that distributed uniformly as a colorant through the entire mass.

The range of tints obtained within the variation of natural feldspars, with the exception of the olive or sea green feldspars, are only

4492°-Bull. 92—16—3

possible of detection where the materials are prepared with the utmost care. Any dirt or dust on the surfaces of the crude feldspar or carelessness in the crushing or grinding process may result in a fused product of a color far inferior to any obtainable by fusing the darkest colored natural feldspar, the olive-green or sea-green feldspars excepted.

The problem, then, resolves itself into one not entirely of obtaining the feldspar of the best natural color, but more especially of guarding against the introduction of impurities naturally associated with the feldspars and also of impurities which may be introduced in the milling.

Plates II and III show the range of color in the natural feldspars.

DESCRIPTION OF SPECIMENS SHOWN IN PLATES II AND III.

In the following list are described the specimens shown in Plates II and III. All of the feldspars shown in Plates II and III, except H and L (Pl. III), fuse to white or colorless glass.

A. Microcline from Carolina Mineral Co. quarry, at Penland, Mitchell County, N. C. For a description of this deposit see location 110, Bureau of Mines Bulletin 53, page 100.

B. Microcline from Johnson mica mine, near Plumtree, Avery County, N. C. For a description of this deposit see location 106, Bureau of Mines Bulletin 53, page 112.

C. Microcline from Barrett quarry, Essex County, N. Y. For a description of this deposit see location 59, page 133.

D. Green microcline from Rutherford mica mine, Amelia County, Va. For a description of this deposit see location 110, page 167.

E. Albite from Sylmar quarry, Chester County, Pa. For a description of this deposit see location 89, page 156.

F. Microcline from Rhodes quarry, northeast of Northville, Fulton County, N. Y. For a description of this deposit see location 64, page 139.

G. Microcline from Kinkel quarry, near Bedford, Westchester County, N. Y. For a description of this deposit see location 68, page 142.

H. Greenish brown microcline from Berry quarry, Auburn, Androscoggin County, Me. For a description of this deposit see location 40, page

122.

I. Transparent albite from Saunders, near Hewletts, Hanover County, Va. For a description of this deposit see location 114, page 169.

J. Microcline from old Perry quarry, Phippsburg Peninsula, Sagadahoc County, Me. For a description of this deposit see location 21, page 110.

K. Microcline from old Claspka quarry near Batchellerville, Saratoga County, N. Y. For a description of this deposit see location 63, page 137.

L. Andesine from Crown Point quarry, Essex County, N. Y. For a description of this deposit see location 58, page 132.

M. Microcline from Eureka quarry, Portland, Middlesex County, Conn. For a description of this deposit see location 50, page 127.

N. Microcline from Claspka quarry near Batchellerville, Saratoga County, N. Y. For a description of this deposit see location 62, page 136.

O. Microcline from Tyrol Mountain quarry southwest of Northville, Fulton County, N. Y. For a description of this deposit see location 66, page 140.

P. Microcline from Richardson quarry, Godfrey, Ontario, Canada.