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William Kent, New York, N. Y.:—The Institute may congratulate itself on the opportunity of reading the splendid address of President Brunton. It is an admirable summary of the progress that has been made in the mining and metallurgical arts in recent years. The paper rightly gives the chief credit for this progress to the aid which has been rendered to these arts by the advances in mechanics, chemistry, and electricity. It is notable that most of the headings in Mr. Brunton's address refer to the work of the mechanical engineer, the electrical engineer, and the chemist, rather than to that of the specialist in mining-operations. It seems that the most successful mining engineer of the present day is the one who makes the most intelligent application of the inventions and designs of engineers and others who are not directly engaged in mining. A tabulation of the headings of the address, grouped as below, shows this most clearly. Work of the Mechanical Engineer—Rock-drills, hoisting-machinery, tramming, pumping, ventilation, dredging, Sampling, concentration, briquetting, fume-recovery. Work of the Electrical Engineer—Electric machinery for hoisting, pumping, tramming, lighting and signaling, electric transmission, electric smelting. Work of the Chemist and Metallurgist—Explosives, chlorina-tion, cyanidation, roasting, lead-smelting, and copper-smelting. Work of the Geologist—Economic geology. Work of the Mining Engineer—Mine-mapping, surface-mining, timbering, tunneling; and planning and supervision of the work in general. The mining engineer of the present day, who is in responsible charge of a large plant, finds his chief work not in doing those things he was trained to do as a specialist, but in making use of the knowledge of geologists, chemists, and electrical and

Jan 1, 1910

By C. R. Hayward, H. O. Hofman

I. INTRODUCTION. THE aim of instruction in a metallurgical laboratory is to make real the principles on which metallurgical processes and operations are based, and to foster the spirit of investigation: The materials with which experiments are carried out are ores, metals, and metallic compounds. The method varies with the end sought. A class may work as a whole, each member contributing his share to the solution of a problem, or the students may carry on investigations independently; the former exemplifies class-research; the latter, individual research. It is with a branch of the former, with special reference to ore-treatment that the present paper intends to deal. In smelting an ore by a well-established process, the result is shown by analyzing the products to see whether their compositions correspond to those calculated in making up the charge; by taking account of stock to show the distribution of metal in the different products made and the losses from dust and volatilization, by casting a thermal balance to find the ,distribution and losses of heat; and by making a cost-sheet to ascertain, as far as possible, the necessary outlay of money. In, lixiviation and amalgamation, the mode of operating has to be varied to adapt a process to the individual ore. Here a number of tests become necessary. Each will consist of a series of experiments with one variable, in order to find the conditions under which the variable gives the best result; a. summary of several tests will give the best method of operating.. Working a number of charges with the best method will furnish the data desired for ascertaining the recovery of metal,

Jun 1, 1909

By E. W. Davis

THIS nation has been depending upon the Lake Superior iron ranges for most of its iron ore requirements for over half a century. Furthermore, it can continue to draw the major portion of its ore requirements from the same source for another century or more, but to accomplish this, great changes must take place in the present ore mining industry. Preliminary preparations for these changes are now underway and in the next few years decisions of far-reaching importance must be made. But to understand the situation, it is first necessary to know something of the nature and occurrence of the Lake Superior iron formation. So far as is known, the merchantable grades of iron ore remaining in the various Lake Superior ranges are as shown in Table 1, which shows that

Jan 1, 1947

By J. B. Morrow

AMONG the most notable of Canada's many contributions to the personnel of the mining industry in the United States is J. B. Morrow, born in Halifax, Nova Scotia, April 9, 1886. Soon after completing his schooling at Dalhousie University in 1906 he emigrated to Arizona and Kew Mexico, via Cobalt and Larder Lake, Ontario. After preliminary experience in sampling and mucking he was employed by the Phelps Dodge Corp., first as chemist at the Copper Queen smelter, then, in 1908, with the Corporation's Stag Canyon coal branch at Dawson, N. M., in various capacities fro111 chemist to coke oven and coke department superintendent, and finally as general outside superintendent. While with Phelps he had some contact with the late Dr. Douglas, of whose industrial methods he has always been a great admirer.

Jan 1, 1937

By Betty J. Laswell, Gerald W. Laswell

The stepped-up pace of US open-pit and surface mining during the 1970's is a direct response by mining firms and equipment manufacturers to rising costs and declining ore grades. In the race for bigger and more efficient machines, rotary drills have emerged as the foremost leader in primary drilling at major US surface operations. At least 12 different manufacturers now offer rotary rigs in the 102- mm-diam. (4-in.) or greater blasthole size range. With capital investment for the larger units quickly approaching $1 million, the question is asked, "What's been the performance record to date of rotary drill rigs operating in North America?" To answer that question, a comprehensive study of rotary blasthole drills was conducted which qualitatively reveals various problem areas inherent in the rotary drill market and indicates some new directions for improvement.

Jan 6, 1978

Inflation, fuel shortages, environmental restrictions, and a worldwide recession that sharply curtailed the demand for goods and services, were the main causes for the poor performance & virtually all industrial minerals in 1975. This poor showing was not a surprise. As Felix Shay correctly predicted in his introductory remarks to last year's industrial Minerals Review (ME, Feb. 1975, p. 70), ". . . the minerals industry will soon be facing falling demand as a consequence of sharp declines in auto production, housing, appliances, and other consumer goods. Moreover, when sales weaken. the high-volume, low-priced industrial minerals will incur sharply.

Jan 3, 1976

US 4,181,588 - Direct extraction of lead from lead sulflde ore. Ore is leached with a solution of ferric chloride and sodium chloride. The leach liquor is filtered to remove sulfur and gangue, then cooled in a crystallizer to precipitate lead chloride The slurry from the crystallizer is subjected to electrolysis to deposit lead chloride on the cathode plate. Solution from the electrolysis cell is used in the leaching step. M.M. Wong and F.P. Haver, assigned to US Secretary of the Interior Jan 1, 1980. 6 pp. (204-115). Filed: 1-4-79 (1,026).

Jan 1, 1982

By M. Streat, R. Y. Qassim

Summary This paper reviews the developments in uranium process technology as a result of modern trends in the design of ion exchange equipment. The operation of the Cloete-Streat fluidised bed contactor is described and pilot-plant development of this contactor for uranium slurry work at Imperial College is outlined. The properties of a suitable ion exchange resin for slurry treatment are discussed, together with a description of relevant rheological properties of ore suspensions. A prediction of ion exchange resin- slurry behaviour is presented in order to establish the feasible operating limits for this type of R-I-P contactor.

Jan 1, 1973

Jan 1, 1927

By Geo. T. Lynch

PALEOLITHIC MAN, laboriously shaping a stone implement in his cave, discovered that the dust irritated his eyes and nostrils and hindered his labors, whereupon, muttering a few incantations, forerunners of modern profanity, he removed himself and his work outside. There, ignoring the jeers of the hairy ?old-timers,? he turned his back to the wind and resumed operations in comparative comfort. Thus originated the dust problem in the mineral industries, and its solution. Despite long familiarity with the annoyance, danger, and loss occasioned by dust, little progress was made in the engineering solution of its problems until recent years. Some advance can now be reported but too many traces of ancient tradition and practice still remain. Considerable published information is available but only a part of this is of proved accuracy and utility. The greater portion is either misleading, being derived from too few cases to be of general application, or entirely erroneous, originating in guesswork, legend, or individual inspiration, divine or otherwise. The engineer, confronted with a dust problem, has neither the time nor the special training required to extract the values from this mass of low-grade. It is, therefore, desirable that we attempt to correlate the known values and to put them into a form upon which actual progress can be based. This discussion is, then, for the benefit of that engineer, particularly the engineer in the mineral industries and more particularly in ore-dressing plants, and is merely a gathering of facts already known but difficult to segregate.

Jan 1, 1938

By A. R. Rosenfield, G. T. Hahn

The effects of adding 0.025 volume fraction of uniformly dispersed Tho2, particles (particle size -380A) to iron have been examined. The two-phase alloy is shown to have a lower transition temperature and higher cleavage stress than either the base metal or a solid-solution alloy (Fe-3Si). Enhanced cleavage resistance is thought to be a consequence of particles limiting the effective slip distance of dislocations and thus the ability of Pile-ups to act as stress concentrations. Further calculations predict that the highest cleavage strengths are attained with uniform dispersions, where the particle size is kept small (-250A) and the volume fraction is relatively large (-2 to 3 pct). ALTHOUGH a fine dispersion of second-phase particles is known to impart strength to an alloy, the possibility that it might also impart ductility has only recently been explored. Outstanding progress has been made in the production of ductile tungsten alloys containing Tho21,2or (Hf, Zr)C,= but the contribution of the dispersion to ductility has neither been optimized nor fully analyzed. The basis for such an analysis has now been developed1,5 and is discussed briefly below. Experiments on iron are also described that attempt to isolate one of the possible ductilizing mechanisms and test its effectiveness. In analyzing these experiments, it is important to remember that cleavage obeys a stress criterion, and that either a lower ductile-to-brittle transition temperature or a higher cleavage stress is evidence of enhanced resistance to cleavage. DUCTILIZING MECHANISMS Slip Blockage. Cleavage fracture of polycrystals may be initiated at the intersection of a slip band (or twin) and a neighboring grain or a large (-1 to 5 µ) particle. The slip band generates a stress concentration at its head, and either the grain boundary fractures, the particle fractures, or cleavage is initiated in a neighboring grain. Experimental evidence for this viewpoint is found in metallographic studies8-8 and from the observation that cleavage is usually preceded by yielding.8-11 The potency of a slip band as a stress concentrator

Jan 1, 1968

By H. R. Fife

AN extended study of dustproofing Freeport-seam coal has empha-sized several fundamental features in the successful treating of bituminous coals. The extent of the exposed surface area and its absorption proper-ties for the dust-retaining film were found to be the most critical factors affecting the efficiency of fly-dust prevention. From recently published screen data and specific surface-area measure-ments on United Kingdom coals, an approximation of the surface exposed by mine-run coal and by 1-in. slack was made. The total surface area exposed by an average ton of this mine-run coal was estimated at 3768 sq. yd., while a ton of 1-in. slack represents a total surface area of 8779 sq. yd. with no additions for porosity. It is important in coal treating to consider that in mine-run coal the fraction above 1/4 in. in size represents 79.5 per cent of the total weight, but only 4 per cent of the total surface, while the fraction below 150 mesh contains 47 per cent of the total surface and only 1.2 per cent of the total weight. Also, one should appreciate that, in a 1-in. slack, the domestic stoker fraction (1 in. to 8 mesh) contains 76.3 per cent of the weight and 8.2 per cent of the surface, while the fraction below 150 mesh represents 3.3 per cent by weight and 54.8 per cent by sur-face area. Wax extraction data on 1-in. to 0 slack from mine-run treated Free-port-seam coal showed that the coating was distributed uniformly as a function of exposed surface; hence, nonuniformly on a weight basis. This distribution of the coating on mine-run coal therefore limits the extent of treating that is desirable on bituminous coal at this point in the preparation. The treatment of Freeport mine-run coal before it reached the tipple gave a 70 to 80 per cent reduction of fly-dust in the tipple, a satisfactory treated commercial slack coal, and an indicated change in the trend of tipple degradation. The premium-treated domestic sizes required a supplemental treatment for complete dustproofness.

Jan 1, 1937

By Thomas M. Drown

IN a communication to this Institute at the Baltimore meeting, February, 1879,* on the "Determination of Silicon in Pig Iron and Steel," the method recommended was the treatment of the metal with nitric acid until action had ceased, and then evaporating with sulphuric acid until the nitric acid was nearly or quite driven off After filtration of the siliceous and carbonaceous residue, and washing with hot water and hydrochloric acid, a silica was obtained, on ignition, which was quite pure. Since this paper was read before the Institute, we have had large experience with the method, and * Transactions, vol. vii, p. 346.

Jan 1, 1880

By Richard Borg

The partial molal free energy of Cd in each of the four intermediate phases, Cd3 Cu, Cd8 Cu5, Cd3Cu4, and CdCu2 is determined using the Knudsen vapor pressure technique. Measurements are made also within the two-phase regions, and thus the variation in FCd is now known across the entire phase diagram. The absolute values are all less the 2.0 kcal and increase regularly with increasing Cd concentration. The small absolute value of the free energy precludes the possibility of obtaining highly accurate values; nevertheless, the results are compatible with those previously reported for the liquid phase. Additional results are reported concerning the lattice parameters of the 6, E, and b phases. THE elements Cu and Cd combine to form four intermediate phases which are designated* and E and which include respectively the following inter metallic compounds: CdCu2, Cd3Cu4, Cd3 Cu5, and Cd3 Cu. The extent of each phase with respect to temperature and composition is shown in Fig. 1 which is the equilibrium diagram drawn according to Hansen.1 All four phases are brittle, and most probably are true intermetallic compounds. Only the crystal structure of the 6 phase has been thoroughly investigated.2,3 The structure is cubic and isotypic with y brass. The structure of Cd3 Cu has not been previously reported, It is hexagonal with a = 8.11 and c = 8.76 0.02Å and the structure is presently being determined.* The compounds Cd3 Cu4 and CdCu, have been each previously the subject of a single investigation. Cd3Cu, is presumed to be cubic4 with the space group Fd3m, whereas CdCu2 is hexagonal2 with the C14-type structure. Cu2 Cd is found by X-ray analysis to be hexagonat with lattice parameters a = 5.00A and c = 16.17Å. The material appears to be pure Cu2Cd as all reflections could be indexed on the basis of the single hexagonal structure. These values disagree with those of Kripyakevich and coworkers5 who report a = 4.96Å and c = 7.98Å. Their investi-

Jan 1, 1962

By Morgan Walker, C. D. Watson, Reid W. Bond, D. L. Trax

Common practice in the Mid-Continent until recently was to prolong the natural flow of oil wells as long as possible by agitation, and then swab for a short period until the well was put on the pump. Comparatively recently the gas-lift has superseded the swabbing and agitating period and in some cases encroached on the natural flowing life, particularly where it was evident that the potential oil capacity of the well was greater than the gas supply, or lifting medium. The majority of wells are finished with either 6¼, 65/8 or 8¼-in. casing and connected to a separator through a flow line which is usually 65/8 in. The flow line is generally designed to eliminate sharp turns and has reduced the gas-oil ratio and therefore increased the efficiency in a good many instances. Until recently all wells were allowed to flow without restriction against the possible trap pressure until it was deemed advisable to put them on gas-lift. This resulted in a fairly efficient flow during the early life of the well if the well was rather large but was usually inefficient in small wells and in the later flowing life of large wells, on account of the large area in the casing and therefore excessive slippage. Recently, considerable effort has been made to increase the efficiency of small flowing wells by running tubing to eliminate as much slippage as possible. With large wells there is a considerable trend toward back-pressuring, or beaning to find out whether it is possible to reduce the gas-oil ratios and increase the flowing life. The greater number of fields that have been back-pressured have been produced in that manner through necessity, either to restrict production for proration purposes or, in fields producing by hydraulic pressure, to reduce water encroaching. The recent Cromwell sand development in Little River is an example where both back-pressuring by means of high-pressure traps and beans and flowing through tubing were used to conserve gas, reduce the high gas-oil ratio and prolong the flowing life. It

Jan 1, 1930

By K. R. Evans

The deformation mechanisms occurring in polycrys-talline, commercially pure titanium and a Ti-8 pct A1 alloy have been investigated and compared to earlier results by Levine on high-purity titanium single crystals and by Conrad on commercially pure titanium. In accord with Levine, two consecutive deformation mechanisms are observed to exist below 500°K with the transition temperature between mechanisms, Tc, strongly dependent upon interstitial composition. T, is found to be 210°. 375° -430°, and 450°K for alloys A large number of investigations have been conducted to determine the rate-controlling mechanisms of plastic deformation occurring in fcc and bcc metals. Very few investigations of a similar nature have been conducted for hexagonal metals. In fact, until very recently, magnesium is the only hexagonal metal which has been systematically investigated for determination of the rate-controlling deformation mechanisms.1"3 From these investigations, it was concluded that basal slip below 420°K occurs by the intersection of forest dislocations,1'3 while for prismatic slip the Peierls mechanism is rate-controlling at low temperatures with interstitial compositions of 0.024, 0.42, 0.61, and 1.13 at. pct expressed in terns of oxygen equivalents. The low-temperature mechanism is found to be an impurity obstacle mechanism in contrast to Levine's earlier conclusion of the Peierls barrier. Measurement of the activation parameters for deformation and estimation of the force-distance profile of the obstacles show their retarding force to be effective over longer distances from the obstacle as the interstitial composition increases. and thermally activated cross slip at higher temperatures. 2 The potential technological importance of titanium alloys has prompted recent studies of the deformation and fracture characteristics of titanium and its alloys. 4-8 Levine' systematically investigated the low-temperature deformation behavior of high purity titanium single crystals oriented for either basal or prismatic slip. It was concluded that the Peierls mechanism was rate-controlling at temperatures below 210°K, while above this temperature an undefined mechanism was rate-controlling. Conrad 7,8 concluded from an analysis of the composition dependence of the critical shear stress at 0°K and measurement of the activation parameters that the low-temperature deformation of titanium is controlled by an impurity

Jan 1, 1969

By H. P. Allen

THE Achotla mill of the Cia. Minera de Pe[n]oles is of special interest in that it is one of the few still employing the chloridization process. The ore milled comes from the Suriana mine and consists of both oxide and sulphide, from neither of which can the gold or silver be extracted by a simple cyanide treatment. The mill was built in 1927, after several years of study in the development of the process1, and operated from December of that year until October 1930. Operations were resumed in February 1935, and have been continuous since, treating approximately 5000 tons per month, while the mine is getting up to full tonnage of 6500 tons per month. Transportation Of Supplies The property is in Guerrero, Mexico, some 175 km. by airline southwest of Mexico City. The mill site is at Temisco (Fig. I), 8 km. from the Balsas River and 4.8 km. by aerial tram from the mine. At Temisco are the general office, shops, warehouses and laboratory serving both mine and mill. Here sufficient water is available either from a small creek running through the property or from the Balsas River, also convenient and ample storage space for the tailings. With the exception of the mine timber and a few native building materials which may be obtained locally, all supplies for both mine and mill are brought down the Balsas River from Balsas, the terminal of a Mexican National Railway line out of Mexico City. The method of transportation on the river is interesting. Rapids with very fast water are numerous, prohibiting the use of mechanically propelled boats. Those used resemble large, flat-bottomed rowboats some 22 ft. long by 8 ft. wide (Fig. 2). They are manned by two oarsmen sitting in the bow, each handling one large oar, and usually another man in the stern who, with his oar, assists in steering the boat, especially when the rapids are run. From 3 to 7 tons of freight are carried on each boat, depending upon the stage of the water, which governs also the time

Jan 1, 1937

By T. S. Lundy, R. E. Pawel

Effects of short-circuiting paths on observed diffusion behavior in real crystalline systems are considered. It is concluded that experimentally measured diffusion coefficients may vary widely from values associated with true lattice diffusion to those appropriate for short-circuiting paths alone depending upon the conditions of the experiment and the sensitivity and completeness of the data. IN 1961 Harrison1 classified experimentally observed diffusion behavior in systems involving both lattice and dislocation-enhanced atomic transport into three categories. His types A and C were limiting cases where the measured diffusion coefficients using the usual serial sectioning techniques were representative of lattice diffusion (with only slight effects of dislocations) and dislocation-network diffusion (with only slight effects from lattice diffusion), respectively. In both cases A and C for a sectioning experiment in which the diffusion couple has the semi-infinite geometry and unidirectional diffusion takes place from a plane source located at the origin of the coordinate system, he pointed out that Gaussian penetration behavior should be observed. For case A the lattice coefficient should be slightly enhanced by dislocation contributions, and the model of Hart2 can be used to predict the amount of this enhancement. For case C the observed coefficient should be that for the dislocation network and have little or nothing to do with lattice diffusion. Hart's model in its general form is still applicable, but the apparent diffusion coefficient for this case is virtually independent of dislocation density. Harrison's case B is that for which non-negligible contributions exist for transport by both mechanisms and "the concentration distribution does not approximate to any simple form." With the possible exception of very low temperatures where diffusion distances approach atomic dimensions, any real diffusion specimen will in general show non-Gaussian behavior provided the data are complete enough to uncover it. Thus, a "complete" set of data for any real system cannot be expected to be totally amenable to treatment by a simple mathematical model which does not take into account the relative distribution of transport by the various modes or submodes. For a particular sensitivity of specimen analysis and at a given temperature of annealing if the concentration profile could be observed as a function of time, "the behavior will initially be type C, and will develop into type B. and ultimately type A".1 Thus, it appears that the type of diffusion behavior which is experimentally observed in a given system depends very much upon the particular experimental conditions and the particular tools available to obtain the data. Interpreted in this fashion, Harrison's classification refers not to the diffusion behavior as a whole but to the relative sensitivity of the method of examination and completeness of the data. In the present paper we will: 1) assume that the measured penetration behavior follows the same general classification as that proposed by Harrison; 2) give, for diffusion in tungsten, examples of the range of diffusion coefficients that it is possible to obtain in a single experiment; and 3) speculate that some arguments which consider the possibility of short-circuiting effects being responsible for "anomalous" diffusion in several bcc metals may have been discarded prematurely.3 Both monocrystalline and polycrystalline tungsten were used in this work. The former was obtained as triple-pass, electron-beam zone-refined 6.0-mm-diam rod from Materials Research Corp.. Orange-burg. N.Y. The latter was swaged, high-purity bar stock which was annealed for 2 hr at 2200°C and 10-9 torr to yield an average grain diameter of about 25 /i. The tracer Nb95 was received in oxalate solution from the Isotopes Division, Oak Ridge National Laboratory. Experimental procedures of specimen preparation, isothermal diffusion annealing, serial sectioning by anodizing-and-stripping, and y counting of the individual sections to determine the tracer penetration profile after a given diffusion anneal have been described elsewhere.4 However, it should be noted that the anodizing-stripping sectioning technique has the particular advantage for this research of permitting sectioning to be accomplished over a wide range of

Jan 1, 1970

Air-sand Process of Cleaning Coal Discussion of paper by THOMAS FRASER and H. F. YANCEY, presented at the New York Meeting, 1926, and issued, as Pamphlet No. 1561-F, with MINING AND METALLURGY, February, 1926. T. DEVENNY, Edgarton, W. Va.-How near the size of the sand can the coal to be treated be brought? Do you use an 8-mesh coal on that cleaner? J. J. RUTLEDGE, Baltimore, Md.-From the little I have seen of the apparatus in operation, I should say 8-mesh. In my experience in metalmine concentration work, trying to separate different minerals on one jig, sometimes I have succeeded and sometimes not. This apparatus has appealed to me; something of this kind should be useful with the silicates and carbonates of zinc. I think this apparatus has possibilities in metal mining. Recently in our coal field a screen has been introduced for cleaning coal; it is giving excellent service. When I asked the inventor why he did not take it to the metal mines, he said there was a good and sufficient reason, in a patent way. There may be reasons why it would not be applicable for metal mining; but the simplicity of it appeals to me and I cannot see why it could not be so used. T. FRASER (written discussion).-We feel that 8-mesh would be about -the minimum size of coal practicable to treat by the air-sand process. This would depend partly upon the friability of the coal. The more nearly the lower size limits of the coal- approaches the size of the sand, the more .time will be required in screening the sand out of the cleaned coal, which would mean a little more chance of breakage. In regard to the treatment of ores; this would necessitate the use of some heavier mediums than ordinary silica sand, or some other means of making the separation at a higher specific gravity than is required for coal. We are now working on a method of obtaining this effect for the preparation of anthracite coal without resorting to the use of heavier and more expensive material than common sand.

Jan 1, 1927

By Benjamin Petkof

The mineral mica, which has been known to man since ancient times, has played an impor¬tant role in the development of our modern industry. In the latter part of the 19th century sheet mica began finding use as a dielectric insulating material in the newly developing electrical industry. Later, when modern elec¬tronics began to develop, it became a vital insulating and dielectric material for use in electronic equipment. Both the electrical and electronic industries were greatly dependent on some form of natural mica. The manufacture of electric motors of varying sizes, electronic tubes, and other electronic items was dependent on an adequate supply of sheet mica. During World War II this material was so vital to national defense that special efforts were made to mine it in the United States as well as to obtain it from overseas mica-producing areas. However, advancing technology has successfully begun the progressive development of man-made mica-based and non-mica-based materials that can replace mica for many uses. In addition, developing technology has dictated changes that have made sheet mica unnecessary for some uses. As the demand for sheet mica declined, the demand for scrap and flake mica has continued to increase. In fact, today the domestic production and use of scrap and flake mica far outshadows the necessity for good¬quality sheet mica in this country. Historically the United States has always been dependent on foreign sources of material for good-quality sheet mica and imports practically its entire requirement. In the case of scrap and flake mica, the United States is the dominant world producer and consumer. End Uses Sheet mica (Chowdhury, 1941; Rajgarhia, 1951; Skow, 1962) is available in many com¬mercial forms, but these forms can be broadly classified into manufactured and unmanufac¬tured mica. Manufactured mica consists of mica that has been shaped, punched, or other¬wise processed into some form, suitable for a particular end use. Unmanufactured mica con¬sists of partially hand-trimmed or processed material that has not been prepared for any particular end use. Unmanufactured mica is broken into two commercial classes consisting of sheet mica and scrap and flake mica. These classes of mica differ greatly in their ultimate end uses and marketed forms. Sheet muscovite mica can be classified by color, degree of prep¬aration of the crude material, thickness, size, visual appearance, and electrical quality. In addition, phlogopite mica is also classified by its thermal stability. Scrap and flake mica consist of mine, trimming shop, and factory scrap that occurs as remnants from mining, processing, and manufacturing operations, and small particle size mica that is available from the beneficiation of pegmatites, clays, schists, or other mica-rich host rock. The end uses for sheet mica vary so greatly from those of scrap and flake mica that it is necessary to discuss them separately. Sheet Mica Sheet mica consists of relatively flat sheets of material which have been mined as naturally occurring books or runs of mica. These sheets are hand-trimmed to remove any imperfections and are punched or stamped into specified shapes for industrial use. Sheet mica can be further processed and is described or specified as block, film, or splittings based on thickness. Block mica is not less than 0.007 in. thick with a minimum usable cross-sectional area of 1 sq in. Film mica is split from the better quali¬ties of block mica to specified thickness groups ranging from 0.0012 to 0.004 in. Splittings are sheets of mica with a maximum thickness of 0.0012 in. and a minimum usable area of 0.75 in. Other small sized, lower quality block mica

Jan 1, 1975