QUARTZ (obscurely crystalline.)
LOANED BY FOOTE MINERAL CO.
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.)
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 from Australia and a few from Brazil. In present usage bloodstone is the “birth stone” of the month of March.
“Who on this world of ours their eyes
In March first open shall be wise,