Carnotite and uraninite or pitchblende as mined for ores are generally more or less mixed with other materials and are rarely found pure. The uranium in the ores is usually stated commercially, for convenience, in the form of the uranium oxides represented by the formula UO2 + 2UO3, briefly expressed as U3O8. Most carnotite ore varies from 1 per cent. to 3 per cent. of U3O8; a 5 to 10 per cent. ore is considered high grade; a 20 to 40 per cent. ore is remarkably rich. Uraninite and pitchblende ordinarily contain more uranium than carnotite contains, and even in the impure forms in which they are mined as ores, they often show this greater uranium content. The ordinary uraninite and pitchblende ores carry from 2 to 3 per cent. to 8 or 10 per cent. U3O8, and a 20 per cent. ore is very high grade, though some ore runs 60 or 70 per cent.
Carnotite.
—Carnotite is an amorphous, soft, powdery material, sometimes more or less coherent and of a talcose or waxy character, generally of a brilliant canary yellow color, though sometimes discolored by iron, organic matter and other substances. It is essentially a hydrous potassium uranium vanadate. Some authorities believe that carnotite is not a distinct mineral, but a mixture of different minerals.
Uraninite and Pitchblende.
—The terms uraninite and pitchblende are often used synonymously to designate the same mineral, but more properly the term uraninite is a general name for all forms of the mineral and especially for the purer and distinctly crystalline variety, and the term pitchblende is applicable to the impure amorphous form. It is black or grayish black in color, opaque, and often has a submetallic glossy or pitchlike luster. Uraninite is often remarkably lacking in distinctive characteristics, so that its presence might frequently be overlooked. For this reason it seems possible that this mineral, now known in only comparatively small quantities, may some time in the future be found more abundantly.
Uraninite, like carnotite, has a somewhat indefinite formula, but is essentially a combination of the two uranium oxides UO2 and UO3, in which UO2 seems to act as a base and UO3 as an acid. A number of both the rarer and commoner elements are often associated with them. The relative amounts of the two oxides vary considerably in different specimens, especially in the impure form of pitchblende, and no definite formula can at present be given. In pitchblende a notable amount of water, perhaps sometimes in chemical combination, is often present. Several other minerals much rarer than uraninite or pitchblende are related to them in composition, among them being cleveite, bröggerite and nivenite.
Other Ores.
—Though carnotite, uraninite and pitchblende are the most abundant of all the radium and uranium materials in nature, and produce almost all the radium and uranium of commerce, yet many other minerals contain both metals, and though as yet known only in such limited quantities as to be of small commercial value, may in the future be found in quantities of importance. Among them may be mentioned tyuyamunite, a hydrous calcium uranium vanadate often associated with the hydrous potassium uranium vanadate described above as carnotite; autunite, a hydrous calcium uranium phosphate; torbernite or chalcolite, a hydrous copper uranium phosphate.
GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION OF RADIUM AND URANIUM
The only regions of the world that have as yet produced any large amounts of radium and uranium minerals on a commercial scale are Colorado, Utah and Austria. Cornwall, Australia and Germany have produced a small quantity of these minerals. They are known in small quantities in France and Portugal, and have been reported in India and German East Africa, but in these regions they have not yet become commercially important. They occur sparingly, so far as yet known, and practically as only mineralogical curiosities, in Connecticut, North Carolina, Canada, Norway and many other regions, but may in the future be found in larger quantities.