=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