Back Aa

Birds and Nature, Vol. XI, No 2, February 1902

<h2 id="c14">QUARTZ.</h2> The crypto-crystalline (obscurely crystalline) varieties of Quartz are many. The following may be named as the most important: Chalcedony, carnelian, sard, chrysoprase, prase, plasma, bloodstone, agate, onyx, sardonyx, jasper, basanite, flint and hornstone. The distinctions between the different varieties are loose and are differently stated by different authorities. Some class agate, onyx, sardonyx, plasma and carnelian together as varieties of chalcedony, while others consider chalcedony a simple variety. The chalcedonic varieties of quartz agree in having a fibrous structure and in being somewhat softer (hardness 6½) and somewhat lighter (specific gravity 2.6) than crystallized quartz. They also break with more difficulty than quartz, being very tough. The varieties differ among themselves, chiefly in color. Common chalcedony has a waxy luster and is usually translucent rather than transparent. The transparent forms are known as “oriental,” the translucent as “occidental” chalcedony. Common chalcedony has little color, shades of gray and blue being the most common, although other tints occur. It usually presents rounded surfaces which have grape-like, kidney-like or stalactitic forms. It occurs coating other rocks or minerals or lines cavities or fills veins and clefts. It is never, so far as we know, deposited in any other way than by percolating waters. At Tampa Bay, Florida, the waters containing chalcedony have penetrated corals and preserved them, often giving forms showing the shape of the coral outside and a cavity within. Throughout the “Bad Lands” of the West, clefts in the hills are often filled with sheets of chalcedony varying in thickness from that of thin paper to nearly an inch. These chalcedony veins ramify in all directions and often extend for many rods without interruption. When the chalcedony is penetrated by branching forms of manganese or iron oxide the forms known as “mocha stones” and “moss agates” are produced. These are not due to vegetation any more than the similar forms of frost on our window panes. They are purely mineral in their origin. Moss agates are found in numerous localities in the States of Utah, Wyoming, Colorado and Montana. In the opinion of Mr. George F. Kunz “no stone that is used in jewelry in the United States is cheaper, more beautiful or more plentiful than the moss agate.” The best occur as rolled pebbles in the beds of streams. The name, “Mocha stone,” sometimes applied to moss agates is either due to the fact that those first used came from Mocha in Arabia, or it is a corruption of the word moss agate. The finest moss agates now known come from India. A white variety of chalcedony containing minute blood red spots is known as St. Stephen’s stone. Chalcedony was formerly used much more and more highly prized than at the present time. It was especially employed for seals and rings, but also for plates, cups and vases. These were often engraved in the most elaborate manner, the hardness and toughness of the stone making it well adapted for this purpose. The sentiment of the stone is: “A disperser of melancholy.” The name chalcedony is from Chalcedon, a city in Asia Minor, where the original chalcedony was found. This mineral was probably not like our modern chalcedony, however, being more probably a green quartz. This chalcedony is mentioned as one of the foundation stones of the Holy City in the Book of Revelations. <div class="fig"> id="fig5"> <ANTIMG src="images/i11204.jpg" alt="" width-obs="500" height-obs="655" /> QUARTZ (obscurely crystalline.) LOANED BY FOOTE MINERAL CO. </div> <dl class="undent"> Left column: Bloodstone, polished (India.) Tiger Eye, polished (South Africa.) Center: Chrysoprase, polished (Arizona.) Agate and Carnelian, polished (Lake Superior.) Right column: Jasper (Germany.) Ribbon Jasper, polished (Siberia.) <div class="pagenum" id="Page_77">77</div> Carnelian is a red variety of chalcedony, sard a brown variety. All gradations between these shades of course occur, those of the reddish cast being the most common. The most highly prized color for carnelian is a deep blood red, appearing darker red in reflected light. The lighter red and yellowish shades are less desirable, stones of these shades being known as “female carnelians,” while those of the darker shades are known as “male” carnelians. The colors are due to oxides of iron and can sometimes be changed by heating. Thus the yellowish and brownish carnelians being colored by iron hydroxide can be changed by heating to red, the water being driven off and iron oxide left. The heating may be done in the sun or by some other slow means. Even olive green stones are changed in India to red by this process. The color may also be introduced artificially by allowing the stones to lie in a mixture of metallic iron and nitric acid, or of iron sulphate for a while. In this way the iron salt needed for the coloring matter can be absorbed by the stone and this is changed afterwards to oxide by heating. The best carnelians come from India, but good stones are also obtained in Siberia, Brazil and Queensland. Carnelians are cut usually in oval and shield-like shapes and were much employed by the ancients for intaglios. They believed them to have the power of preventing misfortune and they were much worn as charms. Sard of typical brown color is much rarer than carnelian and possesses a high value. In other respects it is like carnelian. The sardius mentioned in the Bible as forming one of the stones of the High Priest’s breastplate was undoubtedly a carnelian. The name was derived from Sardius, a city of Lydia whence fine carnelians are obtained. The name carnelian is according to some authorities derived from the Latin word caro, carnis, flesh, and refers to the color of the stone, or according to others it is from the Italian word carniola which has the same meaning. Chrysoprase and Prase are terms applied to an apple green to bright green chalcedony or compact, jasper-like form of quartz. Some authorities, however, call the green chalcedony plasma and restrict the term chrysoprase to the green compact quartz. The terms cannot be accurately distinguished. Most chrysoprase now in use comes from localities in the province of Silesia in Germany, where it occurs in thin layers and veins in serpentine. The green color here is due to nickel oxide which is present in the stone to the amount sometimes of one per cent. The first discovery of the stone is said to have been made by a Prussian officer in 1740. The stone was especially fancied by Frederick the Great so that he had two tables made of it and used it frequently in mosaics. The color fades with light and heat, but it is said can be restored by burying the stone in moist earth for a time. Beautiful chrysoprase comes from India and there are a few localities in our own country where it is found, it being usually associated with nickeliferous deposits. The name chrysoprase comes from two Greek words meaning golden leek and refers to the color of the stone. Plasma, as already stated, is a name applied to green chalcedony, or by some to green jasper. The name comes from the Greek for image and shows that the stone was largely used for seals and other engraved work. Most of that known at the present time comes from India and China. Bloodstone is a variety of plasma containing spots of red jasper looking like drops of blood. Another name for bloodstone by which it was chiefly known by the ancients is heliotrope. This name is derived from two Greek words meaning “sun turning” and refers to the belief that the stone when immersed in water changes the image of the sun to blood red. The stone was often used by the ancients for carvings representing the head of Christ, and one fine specimen of such work may be seen in the Field Columbian Museum. The ancients had a tradition that the stone originated at the crucifixion of Christ from drops of blood drawn by the spear thrust in his side falling on a dark green jasper. The stone takes a beautiful polish. To be of the best quality it should have a rich dark green color and the red spots should be small and uniformly distributed. The supply is obtained almost wholly from India, especially from the Kathiawar Peninsula west of Cambay, whence agate, carnelian and chalcedony are also obtained. Fine examples have also come 78 from Australia and a few from Brazil. In present usage bloodstone is the “birth stone” of the month of March. <div class="verse"> “Who on this world of ours their eyes In March first open shall be wise, In days of peril firm and brave And wear a bloodstone to their grave.” </div> Agate was described in the June number of this magazine. Onyx and sardonyx are varieties of agate in which the layers are in even planes of uniform thickness. This structure enables the stone to be used for engraving cameos. As is well known, these are so made that the base is of one color and the figure of another. This art of making cameos reached a high degree of perfection among the Romans and many superb examples of it have come down to us. The word onyx means a nail (finger nail) and refers to some fancied resemblance, perhaps in luster, to the human nail. Sardonyx is a particular variety of onyx in which one of the layers has the brown color of sard. Other kinds of onyx are those known as chalcedonyx and carnelionyx in reference to the color of the intervening layers. So-called Mexican onyx is composed of quite a different mineral from the onyx here considered, it being made up of calcite rather than quartz. Mexican onyx can be scratched easily with a knife while quartz onyx cannot. Mexican onyx has, however, the banded structure of quartz onyx and it is in allusion to this undoubtedly that the name has been applied. A sardonyx upon which Queen Elizabeth’s portrait was cut constituted the stone of the famous ring which she gave the Earl of Essex as a pledge of her friendship. It will be remembered that when the Earl was sentenced to death he sent this ring to his cousin, Lady Scroop, to deliver to Elizabeth. The messenger by mistake gave it to Lady Scroop’s sister, the Countess Nottingham, who being an enemy of the Earl’s did not deliver it to the Queen and the Earl was executed. On her deathbed the Countess confessed her crime to the Queen, who was so infuriated that she shook her, saying “God may forgive you, but I cannot.” The onyx is the emblem of conjugal felicity and by some is made the “birth stone” of the month of July. It is one of the stones prescribed for the ephod of the Jewish High Priest. The sardonyx was supposed by the ancients to be a different stone from the onyx. To it was ascribed the property of conferring eloquence upon its wearer. It is mentioned in Revelations as one of the stones forming the foundations of the Holy City. Onyx and sardonyx which come from the Orient are esteemed of much higher value in trade at the present time than those prepared in Germany. There seems to be no good reason for this, however, as the latter can be so skillfully made that it is impossible to distinguish them from the Oriental stones. Jasper is a name which includes in general nearly all varieties of impure opaque colored crypto-crystalline quartz. In color it may be red, yellow, green, brown, bluish and black. To many of the pebbles found on almost any sea or lake shore or in the beds of streams the name jasper may properly be applied. If it occurs banded, that is, in stripes of different colors, it is known as ribbon jasper. The different colors of jasper are due to the different impurities it contains. These may be clay, iron oxides or organic matter and at times reach a quantity as high as twenty per cent. The color often varies irregularly in a single stone, giving different effects and sometimes imitating paintings. Jasper which can be used in the arts is very widely distributed. Good red jasper is obtained in Breisgau and near Marburg in Germany. Much of the brown jasper comes from Egypt. What is known as “Sioux Falls jasper” from Sioux Falls, South Dakota, is chiefly of a brown color. This stone was highly prized by the Indians for its color and is the “jasper” referred to by Longfellow in Hiawatha: <div class="verse"> “At the doorway of his wigwam Sat the ancient Arrow-maker In the land of the Dacotahs, Making arrow-heads of jasper Arrow-heads of chalcedony.” </div> The yellow jasper used for mosaics comes chiefly from Sicily, but as good could be obtained in many places in our own country. The green jasper of the present time is obtained chiefly in the Urals and is to a considerable extent worked there into ornamental pieces. The 79 Chinese prize green jasper highly, the seal of the Emperor being made from it. Some jasper of a bluish shade is found in Nature, but that of a deep blue tinge is always artificially colored by Prussian blue. It is then sometimes known as “false lapis,” that is, false lapis lazuli. Ribbon jasper is found in Saxony, but chiefly comes from the Urals. The qualities which make jasper of use in the arts are its color, opacity and capacity for taking a polish. At the present time it is not much used except for mosaic work and for small boxes, vases and dishes. The ancients, however, prized it highly and used it extensively. It is one of the stones prescribed in the Book of Exodus to be worn in the ephod of the High Priest and also forms one of the gates of the Holy City as described by St. John in Revelations. It is probable that the jasper referred to in these instances was of a dark green color, as this was the tint most prized in early times. Green jasper was also called emerald in some instances. The banded varieties were much used for cameos, specimens of which are still extant. By taking advantage of the colors of the different layers, colored objects were made, such as one which shows the head of a warrior in red, his helmet green and breastplate yellow. Basanite is also known as Lydian stone or touchstone on account of its use for trying the purity of metals. Its value for this purpose depends on its hardness, peculiar grain and black color. Different alloys of gold give different colors on the stone which one soon learns to recognize, and jewelers become very skillful in judging of the fineness of gold by this test. Also if an object is plated, by giving it a few strokes on the stone the different color of the gold and base will be revealed. It is simply a black variety of crypto-crystalline quartz, differing from jasper in being tougher and of finer grain and from hornstone in not being splintery. Flint is likewise an opaque quartz of dull color. It differs from jasper in breaking with a deeply conchoidal fracture and a sharp cutting edge. It is also often slightly transparent and has a somewhat glassy luster. These properties have led to its extensive use by the Indians and by nearly all primitive peoples for the manufacture of weapons and implements. Hornstone is more brittle than flint and has a splintery rather than a conchoidal fracture. A number of other subvarieties of crypto-crystalline quartz occur, but they are not important. Oliver Cummings Farrington. <div style="break-after:column;"></div>

1 of 2

2 of 2

Update Required To play the media you will need to either update your browser to a recent version or update your Flash plugin.