Popular Science Monthly/Volume 41/September 1892/Mica and the Mica Mines
|MICA AND THE MICA MINES.|
By C. HANFORD HENDERSON.
ONE can get little pleasure out of a science until one is tolerably familiar with its nomenclature and terminology. We should make even less than we do out of human history if we were not fairly familiar with the language in which it is written. If the words "institution," "government," "constitution" did not convey correspondingly definite ideas, we should be at a loss to interpret the pages of even our more obvious historians. In natural history it is much the same thing, and it is for this reason, I think, that so many make very little out of it. They never get to feel quite at home among the scientific terms which must needs be used. It may seem like insisting upon a very obvious truth to point out that, when we define or describe a thing in terms unknown to the hearer, we do not define or describe it at all; but nevertheless I believe that it is what Mill would have called a luminous platitude. It is certainly a commonplace more noticeable in the breach than in the observance.
A party of two or three are out on a tramp. Perhaps one of the number is a botanist. He is pretty sure to be besieged with questions: What is this?—What is that?—and all asked in evident good faith. One of the tramps picks up a little beach fern and rushes off to the Linnæus of the party to know what it is. Linnæus looks at it, and answers with all good intentions that it is a Phegopteris dryopteris. The non-botanical member thanks him, perhaps says, "Oh, is it?" as if it were a perfectly intelligible thing to be a Phegopteris dryopteris, and in most cases goes away perfectly satisfied. Occasionally, however, it does occur to him that he is just as wise as he was before, and not one whit more so. These are not imaginary cases. It was from being several times in the position of the non-botanical member that led me to reflect that the function of a definition is to define. Now, who is to blame for this extreme haziness of intercourse, Linnæus or his friend? Perhaps both of them.
In the face of these experiences, it is difficult to answer the seemingly simple question, "What is mica?" To say that it is a unisilicate in which the predominant protoxide is potash and the predominant sesquioxide is alumina, is to say something that is fairly unintelligible to those who are not chemists, and something which even to those who are chemists gives only a bit of classification and partial composition, but in reality explains little about the mineral itself. Any answer that we can give is only satisfactory until we learn to push the question a step further. Gautama well expresses the difficuly when he says in the Light of Asia:
"Shall any gazer see with mortal eyes,
Or any searcher know by mortal mind,
Veil after veil will lift—but there must be
Veil upon veil behind."
But this is a difficulty which besets us on all sides when we question any of the thousand and odd minerals described in Dana, or for that matter when we put questions to Nature in any direction.
In the case of minerals we know enough to perceive that there is much yet unexplained which lies well within the domain of the knowable. But it is as difficult for the mineralogist as for the botanist to give even fair descriptions of the objects of his study, for he so soon runs against his brick wall when he comes to talk about either the physical or chemical properties of minerals. The processes of crystallization are as profound a mystery as the life process itself. We are much in the position of the zoologists of the last century, who named and labeled their specimens without knowing the significance of their relationship.
The name mica is not that of a single mineral, but is a family cognomen, which includes a number of varieties. With the outward attributes of the family we are all more or less familiar, for under the common name of isinglass it forms a small part of the stock in trade of every householder. The family is one of some importance in the mineralogical hierarchy. All are shining members, and are alike in splitting into extremely thin leaves or plates; in being more or less transparent; in being highly elastic; and in having certain ingredients in common. There are seven well-defined minerals which lay claim to the family name, besides an extensive list of relatives which have been formed by alteration on exposure to air and water. The series runs from the compact, glistening mica found in granite and gneiss, through many gradations of hydrous micas, until we reach the ordinary soapstones and clays. But the name properly stops when the mineral loses its glistening surfaces, for then the Latin word micare (to shine) no longer applies. Our German friends call it Glimmer, a name whose significance is readily seen.
The importance of the mica family, however, does not depend alone upon its many varieties and numerous relatives. The micas are an essential ingredient in many of our most wide-spread rocks—such as the granites, gneisses, mica schists, and their relatives, which form the continental backbone in both the Eastern and Western worlds. These rocks in time run into each other through infinite gradations, just as the mica passes insensibly into the soapstone, so that we can nowhere find hard and fast lines in the mineral any more than we can in the biological world. If we wish, then, to think of mica correctly, we must picture to ourselves a long stem with many branches, and somewhere on this stem—perhaps midway between quartz and limestone—a group of closely related minerals of peculiar scale-like structure and glistening surfaces. We must think of minerals as momentary crystallizations in an ever-changing current of inorganic matter, and not at all as fixed and final forms.
When we submit the micas to chemical analysis, we find that they all contain a large amount of silica—whose common representative is ordinary quartz;—combined with certain metallic bases, such as alumina, iron, magnesia, lime, and the alkalies (potash, soda, lithia, cæsia, and rubidia). No one mica contains all these—though there is some truth in the statement that the micas are silicates of almost everything—but the different varieties depend upon the nature and proportion of the metallic bases which combine with the silica. Thus, while common mica is in the main a silicate of potash and alumina, it also contains small quantities of other metals, such as sodium, magnesium, and iron.
There is a partial parallel here between the mineral and the organic world. Silica is, so far as we know, a compound made up of two elements, the gas oxygen and the hard, light, non-metal silicon. It is a substance that is almost omnipresent in the rocks of the world. In organisms, on the other hand, it is the carbon which is the chief element, and about which the hydrogen and oxygen and nitrogen group themselves. Silicon seems, then, to play much the same rolé in the mineral world that carbon does in the organic. In many respects the two elements themselves are similar. But the point of interest lies in their compounds. Fine, crystallized carbon, the diamond, is not readily altered. Nor are its simpler compounds with the elementary gases, such as carbon dioxide, marsh-gas, and cyanogen. But when the compounds become more complex, when carbon unites with all three of these elements, and the molecule contains many so-called atoms, it is correspondingly unstable. The highest development of this complicated organic structure is found in the human brain, and in the rapid changes which go on in these tissues we have, if not the cause of thought, at least its accompaniment. The quality and quantity of thought apparently depend upon the differentiation of these carbon compounds, and the consequent ease and rapidity with which they can decompose and recompose.
Now, we have in the mineral world at least a partial parallel to this general behavior, and one that is well illustrated in the members of the mica family. Silicon itself is never found alone, and the proximate reason for this is readily understood. It is a fundamental law of chemistry that, when two reactions are possible, that one will take place which will liberate the greater amount of heat. Apply this to silicon. When it unites with oxygen, the heat of combination is very great, greater than that produced by the combination of oxygen with carbon, and consequently this reaction would take place in preference to many others, even in preference to the oxidation of carbon. The point is admirably illustrated by the chemical reactions taking place in the Bessemersteel process. The pig iron which is run into the converter consists in the main of metallic iron combined with carbon and silicon. When the blast of air bubbles through the molten metal, it is the silicon which first oxidizes. The flame escaping from the mouth of the converter is small and intensely hot. The spectroscope shows a predominance of the silicon lines. Then the carbon flame appears, less hot and more voluminous—the second choice of the oxygen. Finally, the iron itself begins to burn and the blast is discontinued. Bearing these facts in mind, we would never expect to find free silicon, and we are never disappointed. When the element combines with oxygen, in silica or quartz, we have a simple and extremely stable compound, as with the corresponding carbon compound. At a high heat and in the presence of metallic bases, the silica will readily enter into new combinations, as in the processes of glass-making, but in the simple presence of air and water at ordinary temperatures, it remains unaffected through long ages. "When the silica is united with a metal, such as aluminum, in kaolin and the ordinary clays, the compounds are still very stable, but they are less so than the simple oxide. When, further, there are several metals included in the compound, as in the mica minerals and their allies, the silicate decreases in stability as it increases in complexity, and we have, as with carbon, a readily decomposable compound.
The world has chosen rock as the symbol of. stability, but it has not chosen very wisely, for the majority of rocks are anything but stable.
In the case of the mica family the readiness with which the minerals take up water and part with the more soluble of their components is shown in the many gradations by which they pass through the hydrous micas to the clays and soapstones. It is very noticeable in the mica regions themselves. A mica mine is, indeed, an instructive object-lesson in soil formations. One can almost see the decay of the crystalline rocks going on before one's eyes.
Were the micas only important as a rock constituent, they would doubtless receive very careful study by reason of the many interesting problems which their occurrence and alteration bring up, but in addition to this, their characteristic physical qualities, their transparency, elasticity, laminar structure, luster, comparative infusibility, and electrical non-conducting power, give them a number of applications in the arts, and make them the object of industrial mining. The mica of the market is in nearly all cases the common white mica or muscovite. From its chemical composition it is sometimes known as potash mica, to distinguish it from lithia and other micas, but these names are more common in the laboratory than in trade. Although mica is so widely distributed in Nature, it is only in a few localities and under well-defined conditions that it occurs in large enough plates to be profitably mined. Granite and gneiss both consist of a mixture of the three minerals, mica, quartz, and feldspar (another silicate of potash and alumina), but as ordinarily found, the mica is too thoroughly mixed with the other ingredients, and is in too small masses, to be available. It is only when fissures in the rock have been filled with very coarsely crystallized granite that the mica can be mined with profit.
Such fissure veins occur in a number of localties, notably in Siberia and Norway on the other side of the water; and in our own country, in New Hampshire, in North Carolina, in Wyoming, in New Mexico, in the Black Hills of Dakota, and probably in paying quantities in Alaska. Of late years the importation of mica from the East Indies has been quite heavy and has closed many of the American mines. The recent tariff of thirty-five per cent is leading to their partial reopening.
All these mines are more or less alike so far as their natural features are concerned. The chief differences are artificial, and consist in the methods of mining and handling the mica. The mines of western North Carolina have been largely exploited and may well serve as a type.
As one travels across the State to the westward, one passes over three distinct belts of country: the lowlands, covered by recent alluvial deposits; the middle or Piedmont section, a low plateau underlaid by older sandstones and shales; and, last of all, the western or mountain section, in which the Appalachian system reaches its finest development, and in Mount Mitchell its culminating point. The trend of the rocks, in this mountain section is pretty evenly northeast and southwest; they dip at angles which are generally forty-five degrees or over. There are a few mica mines to the east of the Blue Ridge, but the most of them and the best lie to the west. Once beyond this barrier, and evidences of mica abound on all sides. One sees the sunlight reflected from plates of mica on distant hill-sides, and the glitter of tiny scales in the bed of every brook. These look so much like gold that one is tempted to turn Argonaut, and try to bring again the golden fleece. For Colchis, it is easy to read Carolina. The talcose schists and slates of the eastern escarpment are here succeeded by the oldest crystalline rocks of the continent, belonging presumably to the Huronian or Laurentian period. There are giant upthrows of granite and gneiss, and these are full of fissures carrying the coarsely crystallized matrix in which the pay mica is found.
It must not be thought, however, that all these veins are alike profitable, or even that the same vein can be relied upon for any great distance, for that would be far from the experience of the practical mica-miner. It is indeed impossible, even after this lapse of time, when some of the mines have been worked intermittently for more than a quarter of a century, to reach any general conclusions as to what conditions are most favorable for a profitable mine. Old miners say that this or that indication is a sure sign of a good mine, but the shrewdest of them confess that mica-mining is pretty much like gambling. A certain amount is staked in the shape of labor and supplies, and one gets in return either hundreds of dollars' worth of mica, or perhaps only barren quartz and feldspar.
Many of the veins occur in a fine-grained black gneiss, which passes with the mountain miners under the name of "slate."
The vein generally dips with the bedding of the gneiss, but occasionally it changes abruptly and cuts across the strata. In some of the mines the vein does not come to grass, as the miners say, but only begins some distance below the surface. The veins vary in thickness from less than an inch to ten or a dozen feet, occasionally to as much as thirty or forty feet, but these instances are rare. In places the vein pinches out completely and is practically lost, or is cut off perhaps by a large mass of displaced country rock, known as a "horse."
The contrast between the vein stuff and its containing walls is very striking and often very beautiful. The "slate" is almost black, and is generally clean and glistening, while the vein itself is almost snow-white. This is due to the feldspar with which the fissure is filled. It breaks with a clean, smooth cleavage, and shows on such surfaces a brilliant, pearly luster. The dump-heaps around the mine-mouth are largely made up of this dazzling white feldspar. One is constantly tempted to fill every available pocket with the mineral, to the exclusion of other specimens really more interesting. Interspersed with the feldspar are masses of grayish-white quartz and occasional blocks of the coveted mica.
It would be of the highest value to know how these three minerals got into the vein and arranged themselves in their present form, but, as no direct observation is possible, we can only reason back from such facts as we are now able to observe. The fissures themselves are doubtless simple cracks formed by those shiftings and readjustments which are constantly going on in the surface rocks of the earth. The vein material has evidently been intruded from below and has come in a liquid or pasty condition, but just how it has come, and whether as a uniform mass which afterward separated into the different minerals, or as a mixture in which each mineral still preserved its own identity, we are quite unable to say. The most reasonable supposition is that the material came into the vein in a condition of aqueo-igneous fusion—that is to say, rendered liquid at a comparatively low temperature by the presence of water and great pressure—and that it was fairly homogeneous. The question as to which mineral separated first would seem almost hopeless. Yet there is quite strong circumstantial evidence to show that the mica was the first to form, for the mica is much more uniformly crystallized than either of the other two minerals, and frequently leaves the impress of its lamina on the crystals of quartz. After the mica, the feldspar probably separated; and, last of all, the silica that was left over after the formation of these two minerals, collected into crystals of quartz. This is what we would expect theoretically. The mica is only about half silica, the feldspar a little over two thirds, and the quartz manifestly nearly all silica. The minerals containing the greater amount of metallic bases would naturally separate first.
The location of the mines has been largely accidental. So far as I have been able to learn, the first one opened was the Sinkhole mine in Mitchell County. The spot was marked by the existence of trenches, many hundred feet long in the aggregate, and in places fully twenty feet deep. Large trees growing on the débris indicated that the workings were very ancient. It was supposed that they had been for silver; and when the trenches were reopened at the close of the war, the search was for that metal and not for mica. Silver seems to dominate in the Carolinian dream of mineral wealth, when it is, of all such dreams, the one least likely to be realized. The search for silver being unsuccessful, the mines were again abandoned. The mica that had been thrown out was left on the dump, and soon advertised the real character of the mine. A stock-driver, passing that way, carried a block of it with him to Knoxville, where it attracted the attention of men acquainted with its value. They investigated the matter, emigrated at once to Mitchell County, and began systematic mining for mica. As the mineral was then selling for from eight to eleven dollars a pound, the rewards were considerable, and much enterprise was shown in the development of the industry. The first-comers had the easy and profitable task of simply preparing and shipping the mica that had been already mined, and they enjoyed the further advantage of an undisturbed market. So profitable an enterprise, however, soon attracted others. Many of the hands employed in the mines were also land-owners and naturally concluded, as soon as they had learned something of the business, that it would pay better to work for themselves. They began exploring their own plantations, and as these often contained several hundred or even several thousand acres, the ground for prospecting was extensive. It is a region in which the majority of the people are land-poor. The single-tax project would not be apt to meet with favor there.
Then, as now, the mountaineers were largely guided in their search by the ancient workings. These were probably made by the aborigines, and were also for the purpose of obtaining mica. The old workers could only penetrate as far as the rock was decomposed, and were obliged to stop as soon as solid ground was reached. The imprint of their stone implements may still be seen in the decomposed stuff at the sides of the opening. What these people used the mica for is still problematical. Large plates of it have been found in the mounds of Eastern Tennessee, and would indicate that it had domestic application, or was used for personal decoration.
In the absence of these archaeological landmarks, there are other signs scarcely less unmistakable. On exposure to the atmosphere the feldspar is decomposed, the potash being washed out, and the kaolin left as an insoluble residue. If this be followed up, it is pretty sure to lead to mica, but one can not, of course, predict to what sort of mica.
In most cases the mining has been decidedly incidental in its character, and has been abandoned as soon as water was reached, or as soon as the yield of mica ceased to be immediately profitable. Other mines have had quite a history. Perhaps the most famous of the Carolina mines is the Clarissa, near Bakersville. It was opened soon after the Sink-hole, and is said to have produced more mica than all the other mines in the county combined. Its output is reckoned up in hundreds of thousands of dollars. The vein is from four to twelve feet thick, with an average of about six. It has been followed to a depth of over three hundred feet. The mine is now idle and full of water, although men who know it say that there is as much mica there as ever.
With labor at seventy-five cents a day, the primitive methods of mining are the more profitable. Steam drills have been introduced in a number of the mines, but have proved less economical than hand drilling. I do not know that the relation is strictly that of cause and effect, but their introduction has generally been followed by the closing of the mine. When the vein stuff has been blown down, it is an easy matter to separate the blocks of mica from the feldspar and quartz. When once obtained they are jealously guarded, for a clear block of mica of good size represents a value of many dollars. Each mine has its strong-room, solidly built of logs and constantly kept under lock and key. These blocks of mica are in the shape of rough hexagonal prisms (monoclinic), and if of any thickness are quite opaque. They vary in color from silver-gray and green to a rich, almost ruby brown. This last is known as "rum" mica, and sometimes commands an extra price.
The mica is seldom prepared for market at the mine itself, but is taken to a conveniently located glass-house. This generally means a transportation of several miles. Frequently the mines are on steep mountain-sides, and are only connected with the outside world by the roughest sort of trails. In this case the mica is "packed" down the mountain on the backs of men to the wagon-road in the valley below.
At the glass-house the mica is put into shape for shipment. The blocks vary greatly in size. One from the Wiseman mine, near Spruce Pine, is reported to have been six feet long by three wide. Pieces a yard in diameter have been obtained at the Ray mine, in Yancey County, and similarly large plates have been found in Siberia, but these are exceptional. The average block is little larger than the page of a magazine, and is generally less than six inches in thickness. It separates very readily into sheets parallel to the base of the prism. It is estimated that this cleavage may be carried so far that it would take three hundred thousand of the mica plates to make an inch. It is needless to say, however, that such a thickness is not suitable for service in stoves and furnaces. The mica is generally split into plates varying from about one eighth to one sixty-fourth of an inch in thickness. In preparing these plates for market, the first step is to cut them into suitable sizes. Women are frequently employed in this work, and do it as well as, if not better than the men. The cutter sits on a special bench which is provided with a huge pair of shears, one leg of which is firmly fixed to the bench itself, while the movable leg is within convenient grasp. It is requisite that the shears shall be sharp and true, for otherwise they will tear the mica.
The patterns according to which the mica is cut are arranged in a case near at hand. They are made of tin, wood, or pasteboard, according to the preference of the establishment. Generally they are simple rectangles, varying in size from about four square inches to eighty. The following table, taken from actual use, will give some idea of the numerous sizes cut, and of the theoretical prices which correspond to them. The actual prices are at present about forty per cent less:
The cutter selects the pattern which will cut to the best advantage, lays it on the sheet of mica, and then, holding the two firmly together, trims off the edges of the mica to make it correspond with the pattern. She puts both mica and pattern in their proper place in the case before her. Then she takes up another piece of mica, and finding the best pattern, proceeds to shape the sheet as before. In this way the rough plates of mica are reduced to uniformity and are sorted as they are cut. When the cutter completes her task, she has all the mica piled away in little bundles under their corresponding patterns, while the scrap falls in a glistening heap on the floor.
The cleaning process comes next. The cleaner sits directly in front of a window and must examine each sheet of cut mica by holding it up between her eyes and the light. If there be any imperfections, and there nearly always are, they must be removed by stripping off the offending layers of mica until a clear sheet remains. The cleaning is done by means of a sharp penknife—and considerable discretion. It is quite easy to tear away the entire sheet and have nothing left for one's trouble. Both the cutting and cleaning are tiresome routine operations, yet there is a certain fascination about tearing the mica to pieces that few have philosophy enough to resist. One soon becomes absorbed in the task of seeing just how thin a sheet of mica can be separated, and before one realizes it an hour or more is gone.
Finally, the cut and cleaned mica is put up in pound packages and is ready for the market.
There is an enormous waste in the processes of preparation. One hundred pounds of block mica will scarcely yield more than about fifteen pounds of cut mica, and sometimes it is even less. The proportion varies, of course, with different localities.
The chief use of the cut mica is in stoves, and its comparative cheapness has made possible the luminous—not to say artistic—wonders which constitute the latest and most cheerful creations of the stove-men. In Siberia the sheets of mica are still sometimes used in windows, as they were in the seventeenth century in Philadelphia, when glass was a luxury in the colonies. The sheets are also used in the peep-holes of smelting furnaces, in lanterns, in shades, and in the port-holes on board naval vessels, where the vibrations would soon demolish less elastic glass. Mica is an excellent non-conductor, and of recent years has been cut to some extent into narrow strips for use in the construction of dynamos.
The scrap mica was formerly thrown away, with the exception of a small quantity used as a lubricating material, but it has recently found a market in several new directions. Old waste heaps are being bought up, for a few dollars a ton, and their contents cleaned by being passed through a rough mill. This is simply a rotating cylinder of coarse wire screen with its axis slightly inclined to the horizontal. The scrap is fed into the upper end of the cylinder, and slowly discharges itself from the lower end. As it makes its way from end to end, the sand and trash are supposed to fall through the meshes of the screen. The cleaned scrap is then shipped to Richmond, where it is ground into a coarse powder and distributed to the various industries requiring it. Large quantities are used in the manufacture of wall-paper. The mica produces a sparkling surface which is thought to be decorative, but at best the effect is somewhat bizarre. Considerable amounts are used to produce the snow effects on Christmas cards, and in stage scenery and other tinsel; while smaller packages, under the name of diamond dust, are sold as powder for the hair. Much of the ground mica is sent to France, and this, oddly enough, when the East Indian sheet mica is pressing our own pretty heavily in the home market.
The Latin world used the mica dust to strew over the Circus Maximus, while mediaeval Europe knew the golden and silver scales as cat-gold and cat-silver.
But to go back again for a moment from the glass-house to the mines themselves, there is much of interest in the rare and beautiful minerals associated with the mica. Some of the mines are quite noted for these by-products and are as attractive to a lover of color as to the mineralogist. The mica itself is often the carrier of curious forms. Frequently a mineral makes its way between the laminae of the mica, and is thus forced to grow horizontally instead of normally in three directions. This gives us curious dendritic or tree-like forms which come out finely on holding the mica up to the light. The oxide of manganese is most prone to get caught in this way, and gives delicate tracery of dark brown or black. Sometimes it is a garnet which is thus entrapped, and then we have a brilliant little hexagonal plate of ruby glass, very beautiful and very gem-like. By carefully taking off the outer sheet, we can get the garnet-plate set in mica, and it makes a specimen well worth preserving. Less frequently one finds a thin layer of quartz imprisoned between the mica, or a thin layer of the transparent glassy feldspar known as sanidin. Sometimes the mica itself is microscopically striated, and plays queer tricks with the light, giving iridescent films that might easily be mistaken for soap-bubbles.
But the feldspar is the most promising matrix for the mineral hunter. At the Cloudland mine it is well penetrated with the greenish, yellowish, and bluish hexagonal prisms of the beryl. The precious form of this mineral, the emerald, is seldom or never found in the mica mines. There is, however, an intermediate variety known as the aqua marine, which occurs in the mines around Spruce Pine, and is somewhat esteemed as a gem. As the name indicates, it is of a light sea-green color. It is perfectly transparent, and when well cut makes a quiet but really beautiful gem-stone. Clear crystals of aqua marine are exceedingly rare. It comes commonly as a part of the opaque crystal of beryl.
Intimately associated with the beryl are plentiful sprinklings of blood-red garnets, and the two colorings against the pure white background of the feldspar make a very effective combination. Garnets are generously distributed in nearly all the mica mines, and add much to the beauty of these mineral masses. One day at the Cloudland mine, a large mass of feldspar was blown down, and there in the center of the white and standing face of the vein was a blood-red spot at least six or seven inches in diameter. A giant garnet had been cut squarely in two by the blast, and the blood-red spot was a cross-section of what remained.
In other mines, such as the Tolly Bend in Yancey County, the white feldspar is occasionally covered with patches of dainty pink. It is the mineral rhodonite, a silicate of manganese, and is as delicate as a peach-blow vase.
There are also other accessory minerals which are less striking in appearance, but of greater scientific interest on account of their rarity. Such are euraninite, gummite, columbite, and samarskite, containing the rare metals uranium, columbium, yttrium, tungsten, tantalum, and their allies, which are curiosities even to the chemist. At Spruce Pine, one gets excellent specimens of uraninite, the oxide of uranium. It is a heavy black mineral with a frequent orange-yellow coating of another uranium compound, gummite. The miners take considerable interest in finding the mineral, as it is worth something like a couple of dollars a pound, and it takes a very small quantity to make a pound. The oxides of the metal are used to produce black and yellow colors on glass and porcelain. The peculiarly fine black of Haviland china is due, I believe, to uranous oxide.
The Ural Mountains are the collecting-grounds for the cabinets of Europe. In no other district can one find so many varieties of minerals within the same area. The mountains of western North Carolina are in many respects similar. They probably yield a greater number of rare minerals than any other region in America, and are therefore a favorite tramping-ground for collectors. At the smallest cross-roads post-office one hears of the visit of some well-known mineralogist. Nearly every mountaineer has a few specimens in his treasury, and generally he knows the names of the more characteristic varieties, particularly if they have a marketable value. It is not safe, however, to rely very implicitly upon his classification, for his knowledge is of the most superficial sort.
As commonly taught in our schools and colleges, and as commonly apprehended by students outside, a knowledge of mineralogy consists of a more or less definite familiarity with several hundred minerals, and an ability to recognize the more common varieties on sight, or by means of some readily applied physical test. It is largely a knowledge of separate and unrelated facts, a catalogue, one might almost say, and not yet a body of well-organized truth. We have gathered part of the material of a fine science, and eminent men are now at work building this material into a coherent whole. The curious facts of paragenesis, or the characteristic associations of minerals, and the many problems presented by substitution and alteration, are being carefully investigated. The mysteries of crystallization are commanding attention. The progress along these lines is very encouraging. But a great amount of work still remains to be done. One who comes to the study of minerals at this particular juncture will find it pleasurable, even as a study of separate facts, but he will feel, I think, that a greater pleasure remains for him when these results have been still further co-ordinated. We are still waiting for our Darwin.
- Phlogopite, a magnesia mica, commonly of bronze or copper color.
Biotite, or black mica, a magnesia-iron mica, of dark-green or black color.
Lepidomelane, an iron-potash mica, of black or green color.
Astrophyllite, a rare titanium mica, whose powder resembles mosaic gold.
Muscovite, or common mica, a potash-aluminum compound of varying color, white, gray, brown, green, and even violet or rose.
Lepicolite, or lithia mica, a mineral of pearly luster, and grayish to rose or violet color.
Cryophyllite, a very rare lithium mica, of greenish color.