How different the history of such collections might be if those who do the collecting would spend a few hours learning how to read the stories written in the rocks. Thousands of amateur mineralogists have mastered this easy language, many with little more equipment than a keen pair of eyes, normal curiosity and any of a dozen or more excellent reference books. Collecting, studying and experimenting with minerals can be enjoyed throughout the year, and few avocations offer as much variety, activity and interest.

It has been said that a stone, when examined closely, will be found to be a mountain in miniature. Of many stones this is indeed true. If a fragment of common granite, for example, is viewed under a magnifying glass of reasonable power, its uniform gray or pink surface breaks up into innumerable discrete features. Some take the form of exquisitely shaped crystals, almost as hard as gem stones. Others are soft and can be split into thin sheets. Still others present a milky appearance and break into fragments that assume the spiral shape of a sea shell. In some specimens the minute mountain of granite appears to have been folded, cracked and cemented together again- features reproduced on a giant scale by real mountains. Once in a great while you may have the good luck to find a mineral ore and thus, in miniature, strike it rich. Incidentally, by the time the beginner has analyzed a half dozen stones he will develop much respect for the equipment that the lowly prospector carries beneath his hat. As Miss Elizabeth Morley, a school teacher and amateur mineralogist now living in retirement near Philadelphia, says, "There's a lot more to prospecting than a geologist's pick and grub stake!"

Miss Morley's mineral collection, which includes specimens ranging from talc to diamond, got its start one day in 1922 when one of her eighth-grade pupils asked for permission to demonstrate a crystal radio set before his class. Its galena crystal captured Miss Morley's imagination. When the wire "cat's whisker" was adjusted, music came out of the rock! Miss Morley never quite recovered from the astonishment of that moment, and she decided then and there to learn the how and why of the silvery bit of stone which at that time she could not even name.

In the course of learning that galena shares with a number of other minerals the curious property of conducting electrical currents more readily in one direction than the other, she also learned that it breaks into cube-shaped fragments when struck a sharp blow, that chemically it is a compound of sulfur and lead, that it has a hardness of 2.5 (it can be marked by the fingernail) and a specific gravity of 7.6. But the discovery that converted her to amateur mineralogy was the fact that the mineral kingdom, like the animal and vegetable kingdoms, has a taxonomy of its own which draws a distinction between individuals as sharp as that which locates man in one biological category and his pet fish in another.

Minerals today are classified according to their chemical composition, and beginners in mineralogy are urged to learn the classification system. Under this system most minerals can be labeled as a member of one of the following species: sulfide, oxide, halide, carbonate, borate, phosphate, sulfate, tungstate, molybdate, uranate or silicate. In each species there are thousands of individual minerals-metallic or non-metallic.

All minerals are chemical compounds made up of two or more of the 92 naturally occurring elements. Nine elements account for the great bulk of minerals and indeed for 95 per cent of the earth's crust. They are oxygen, silicon, aluminum, iron, calcium, sodium, potassium magnesium and hydrogen. In addition three others, though quantitatively small, are important components of minerals. These three are carbon, chlorine and sulfur.

Because most minerals are composed of a very few elements, many specimens can be identified at a glance. More than 99 per cent of the specimens collected by the average amateur can be analyzed without elaborate equipment or methods. Others require detailed examination. This usually begins with a test for hardness. The standard scale of hardness, ranging from 1 to 10, is based on the relative hardness of a selected group of minerals. From the softest to the hardest it runs:

Having noted the specimen's hard: ness, the mineralogist next tests for streak. The specimen is rubbed against a small plate of unglazed porcelain or an equivalent material. Usually it makes a streak on the white porcelain surface. This enables the mineralogist to see the true color of the specimen: thus a rock that appears brown to the eye may make a distinctly red mark on the white porcelain. This color, together with the specimen's hardness and other tests, will guide the collector to the identity of the specimen as tabulated in a reference text.

Next an estimate should be made of the specimen's general physical character. Some minerals can be flattened by a hammer, and thus are said to be malleable. Others, such as copper, can be stretched and therefore are ductile. If the specimen can be cut by a knife, like a piece of hard tar, and yet shatters under a sharp blow, it is sectile. Those that bend easily and remain bent are called flexible. Some forms of sandstone exhibit this characteristic. Others are brittle and shatter like glass when struck with a hammer or when bent beyond their yield point. Finally, many minerals, such as mica, are elastic.

The next clue to identification is the mineral's density, which can often be estimated simply by hefting it; no one needs a sensitive balance to tell a block of lead ore from one of gypsum. An advanced amateur can easily construct his own balance for determining specific gravity with reasonable accuracy. Suspend a pan from a hook by a spring or rubber band. Put the rock specimen on the pan and measure the distance between the pan and the table over which it hangs. This distance is designated as N. Then carefully raise a wide-mouthed jar of water from below until the pan and the specimen are fully immersed in the water. The pan of course will rise higher above the table, as the weight on the spring is reduced by an amount equal to the weight of the displaced water. This higher position is measured and designated as N. The specific gravity of the specimen is found by subtracting N from N and dividing N by the difference.

Specific gravities of minerals range from 1.7 (borax) to 8.1 (cinnabar) or more. The specific gravity of sulfur is 2.05; gypsum, 2.3; quartz, 2.66; feldspar, 2.6 to 2.75, talc, 2.8, diamond 3.5. The densities of metals extend over a much wider range. Some of the common ones: magnesium, 1.8; aluminum, 2.5; zinc, 7.1; silver, 10.6, gold, 19.3; platinum, 21.5. Comparing the specific gravity of gold with that of quartz, the major constituent of sand, it is easy to see why the grains of precious metal settle so readily in the bottom of the prospector's pan and why the Jolly balance for determining specific gravity became almost the symbol of the assayer's office during the days of the great gold rush.

Other readily ascertained clues to a mineral's identity are its appearance under light (daylight and ultraviolet), its electrical and magnetic properties, its crystal structure, its taste and its odor.

Minerals reflect, absorb and transmit wavelengths of light according to their chemical structure. Hence each presents a characteristic surface texture and color. Some, like the silvery mineral galena, show a pronounced metallic luster; the color may range from light gray through silver, yellow and dark brown to purple. Others, chiefly the non-metallic minerals, show a glass-like luster that ranges through pearly and silky to glistening. Some are as transparent as clear glass; others appear milky or translucent, opalescent or iridescent.

One of the most striking optical properties of many minerals is that of fluorescence: they glow in vivid, characteristic colors when exposed to ultraviolet light. The phenomenon was first observed as a property of fluorite many years ago. Unfortunately fluorescence is not very useful analytically. Some specimens of a given mineral fluoresce readily while others show little if any activity. Some respond to a limited range of wavelengths in the ultraviolet spectrum and others to the whole spectrum. Save for rare examples such as willemite from the vicinity of Franklin, N. J., which emits a bright green glow, fluorescence cannot be depended upon as an analytical test. Nevertheless, most amateur mineralogists own inexpensive ultraviolet lamps for use in displaying their collection.

A number of minerals exhibit electrical qualities. Galena, as mentioned previously, presents greater resistance to the flow of current in one direction than in the other. Thus it is a rectifier and can be used for the detection of radio waves and related electrical applications. This same property is characteristic of certain compounds of copper, silicon, germanium, uranium and others. Quartz and tourmaline in their crystalline forms show what is called piezoelectricity-an electrical effect produced by squeezing the specimen. This property, plus the fact that quartz is one of the most elastic materials found in nature, accounts for the extensive use of this mineral for generating small alternating electrical currents of constant frequency. Thin wafers of quartz, properly mounted in electrical circuits, can be made to vibrate at rates of 50 million pulses per second, and electrical clocks driven from quartz crystal oscillators keep time accurately to less than a second's deviation per year!

Lodestone is the classic example of a magnetic mineral. This naturally occurring magnet will pick up bits of iron or steel and in other ways behave like a horseshoe magnet. When powdered, its particles cling together, and iron filings sprinkled on paper covering a lodestone arrange themselves in the form of the specimen's magnetic pattern. Other minerals, containing iron, nickel or cobalt, also show magnetic properties- some being attracted to a magnet and others, like lodestone, behaving as a magnet.

As for taste and odor, halite (the prospector's name for ordinary salt) of course tastes salty; many potassium compounds taste bitter; those of aluminum cause the mouth to pucker; many iron compounds have a sour taste; a few varieties of limestone and other compounds of sulfur give off the odor of rotten eggs when crushed; some shales have a distinctive earthy odor; some minerals of arsenic smell like garlic.

A pencil, notepaper and a reference book are all the equipment a beginner needs to start in mineralogy, but as he goes on he will add certain other simple articles and tools. One is a light, strong collecting bag, either of the knapsack type or with hand grips. Then he will want a trimming hammer, with a fiat head for cold-chisel work and a sharp edge for trimming specimens; a cold chisel of tempered steel, about six inches long with a 5/8 inch cutting edge; a magnifying glass with a power of 7 to 14 diameters a pocketknife, a streak plate of unglazed porcelain; chemical reagents, including dilute hydrochloric acid and cobalt nitrate or chloride, and a record book. This last is perhaps the most important item in the mineralogist's entire kit. An exceptionally good record book is available from the Eckert Co.; it provides for entering the complete history of each specimen, including the location where it was found, the date, its characteristics, a description of any experimental work made on the specimen and the results.

Unless one has access to a museum or other institution owning comprehensive collections, a good reference book listing the characteristics of the principal minerals is indispensable. For beginners in mineralogy an excellent work is Minerals and How To Study Them, by .E. S. Dana and C. S. Hurlbut, published by John Wiley & Sons, Inc.

Many amateurs add a camera to their field kit. Often the geological character of the locale from which a specimen is taken helps in its identification. Moreover, photographs taken in the field and associated with the written history of specimens add greatly to the interest of collections.

As the collection grows it invites more elaborate experimental analysis, ranging from the detailed study of each specimen's crystallography to chemical and physical tests with the advanced techniques of the modern laboratory. Some of these may be undertaken successfully by the beginner who has a bit of spare room on his workbench. The simple blowpipe test, for example yields powerful results. It requires a flame (candle, alcohol lamp or Bunsen burner), a small block of charcoal, a little powdered borax, a short length of nichrome wire and a tapered blowpipe. Blowing into the tube, the worker directs the flame onto a small fragment of the specimen lying on the charcoal block. The fusibility of the mineral is a clue to its identification; some minerals are readily fusible and others resist the hottest flame. The flame of the blowpipe is made up of two concentric cones, the outer one pale violet and the inner a bright blue. The inner cone is deficient in oxygen. When subjected to the heat of this cone, many metallic oxides give up their oxygen to the burning gas and are thereby reduced, or refined. Conversely the outer cone is rich in oxygen and will, therefore, oxidize many minerals. Such oxides differ in color from the original mineral, and reference book list these changes along with the other clues to the specimen's identity.

Similarly many specimens react characteristically when immersed in a solution of hot borax. To make this test small loop is formed at the end of the nichrome wire. The loop is brought t a yellow heat with the blowpipe, dipped into the powdered borax and returned to the flame, where the powder adhering to the loop is melted. The red-hot globule of melted borax is then dipped into a crushed sample of the specimen and returned to the flame. As the sample enters into solution with the borax it reacts chemically and a characteristic color appears which changes, often radically, as the globule cools.

Within a surprisingly short time the beginner will learn to identify a large number of the rocks in his locality. He will meet or communicate with other collectors and exchange specimens not available in his immediate vicinity. And if he has a flair for experimental chemistry, he will discover that nature has stocked almost every hillside with an assortment of raw materials rivaling those carried by many supply houses-all free for the taking.

Where did these compounds originate? Under what conditions? How much time did nature lavish on their formation? In seeking answers to these questions the amateur may be lured into the broader field of geology-in which he will come to observe at first hand the frozen remains of creatures that disappeared from the earth long before the advent of man, to explore the ooze of ancient seas, to examine the explosive forces that have shaped our planet.

TO ENJOY the ownership of a home-made astronomical telescope it is not essential to equal in skill, means or equipment the experienced builders of some of the larger, more elaborate instruments that are described in this department. Almost as much fun may be had with a much simpler instrument. The following are descriptions of two telescopes which can almost be built on a kitchen table.

C. G. Stratton of the State Teachers College, River Falls, Wis., writes: "I have followed your amateur astronomy articles with great interest for many years. My modest but workable telescope was made by a beginner without access to a machine shop. Its six-inch mirror was made by my son Bill while in college. Having retired from teaching, I undertook the project of mounting it. Because trees and street lamps prevent the use of a telescope at home, it was designed to be portable. The mounting was made from 15-inch pipe fittings. A local blacksmith welded a six-inch circular plate to the T for the polar axis and another to the pipe cap at the end of the declination axis, slightly dishing both plates. The shims are of tin. Before assembly the plates were ground together with Carborundum grains to gain a fairly continuous contact. The result was surprisingly good.

"The tube was made by the local tinner and is not a very good job. A stub tube holds the mirror and, being slightly larger than the main tube, slips over it. Thus it is easily removed for dustproof storage.

"Due to inexperience and uncertainty about the exact focal length of the mirror, I mounted the prism in a sleeve six inches long which fits snugly inside the tube and can be moved lengthwise in it.

"The prism is a l-1/2 inch section sawed from a war-surplus prism of greater width. The position of the eyepiece holder also is adjustable. It is mounted on a tin slider that uncovers a series of holes in the tube. It was well that these precautions were taken, as it was found that the focal length of the mirror was slightly less than was thought and that it was necessary to use two of these holes, one for the Ramdsen eyepiece and one for the Huygenian."

The tube of the Stratton telescope (see drawing) rests in a wooden cradle in which it may be rotated freely to make the eyepiece accessible in all positions of the instrument, a luxury not afforded in many more elaborate ones. The builder cites as a mistake the position of the finder, which should be close to the eyepiece. It was made of war-surplus lenses mounted in brass tubing from a bathroom fixture. Despite its chromatic aberration, it is efficient.

A TELESCOPE finder of a type not known to have been used by amateur astronomers is described by Stanley B. Rowson of Kansas City, Mo. "It is an adaptation," he says, "of the 'split pupil collimator' designed for aerial celestial navigation. The eye lens is a simple convex lens of three or four inches' focal length, cut exactly in half and mounted in a simple wooden block. The sight is placed exactly at the focus of the lens. The eye is placed so that the star being found is seen just over the lens while the sight is seen through the lens. The projected junction of the two diagonal lines on the sight is made to coincide with the star as seen over the lens.

"The chief advantage of this finder is the fact that the eye placement is not critical. Because the sight is at the focus of the eye lens, the light from the sight leaves the eye lens in parallel lines. Therefore the apparent direction of the sight, and of the star, is the same no matter where the eye may happen to be behind the lens. This finder has been very satisfactory. Because it is so small, it can be mounted near the top of the tube and sighted with a minimum of stooping and neck-wringing."

To the illustration of Rowson's finder (left), Roger Hayward has added one of a of somewhat more elaborate modification (below). He writes, "You look at the star through the concave side of the lens as shown. Since the lens has no power, the star appears in its usual place. Close to the face and at the focus of the concave side of the lens you place the cross hairs-big threads for night work. As a result you see reflected in the lens an image of the threads, apparently at infinity. It is best to place the eye at about the center of curvature of the lens, which is twice the focal distance. Ideally the lens should be half-silvered. Practically, if the sight is used against a dark sky and the threads are quite luminous or are illuminated from the side, the four per cent reflectivity of the one surface of the lens will be adequate. A meniscus negative lens also can be used, although the star field will be slightly diminished. A focal point for the threads can easily be found where there will be no parallax between the stars and the threads even when the eye is looking through any part of the lens."

THE STRATTON telescope described above has an equatorial mounting- one slanting axis parallel with that of the earth, so that once the tube is set in declination, only one axis need be used in following a star. If the same axes are respectively vertical and horizontal, both must be manipulated to keep the star in view. This is the altazimuth mounting, by some regarded as a step backward. One champion of the altazimuth mounting is F. J. Sellers, prominent in the British Astronomical Association. Thirty years ago, after building and using half a dozen different mountings, none of which had been portable and at the same time rigid, he built an altazimuth, found it good and described it in The Journal of the British Astronomical Association. Later he became widely known for his astronomical work and as the builder and user of on of the five spectrohelioscopes in Great Britain. So well do Sellers and others in the Association think of the mounting that the original description has been reprinted in The Journal, and so well does this department think of it that we are presenting here a drawing of it (), made by Hayward from the original.

The two supporting lengths of tubing have enlarged ends that act as rollers. The observer sits with his knees under the tube, his left hand twisting and rolling the nearer rod away from him on the ground as the observed object moves across the sky. His right hand makes an occasional excursion to the hand wheel welded to the altitude screw. By extending the legs of the tripod or by spreading them forward, or both, the telescope can be quickly aimed at any object and kept smoothly and exactly on it.

The greatest advantage of this mounting is its freedom from vibration. Sellers says that "the rigidity is such that the hands may rest upon the controls during observation without causing vibration." As the hands are the greatest source of vibration in conventional telescopes, this says much in favor of his design. The basic reason for the freedom from vibration is that the tube is supported at its ends, while most others are supported at the middle with the ends free to vibrate.

"The smoothness of working and rigidity of this mounting are quite remarkable," Sellers says. After much experience with telescopes he concludes that "for purely observing purposes, apart from photography, with an eight-inch or ten-inch Newtonian reflector, a convenient altazimuth mount with slow motions is generally more convenient and efficient than an equatorial one."

The screw is a dining-table screw of pitch about half an inch, of a kind in use in Great Britain. As substitutes piano stool screws or old-fashioned auto mobile jack screws are suggested though their pitch is somewhat less. A screw of fine pitch would be a nuisance. In his drawing Hayward has substituted for the original a type of ball and socket joint that he once used on a spectrometer. It can be made to grasp the ball very snugly.

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