Online Encyclopedia

Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.

PITCHBLENDE, or URANINITE

Online Encyclopedia
Originally appearing in Volume V21, Page 663 of the 1911 Encyclopedia Britannica.
» Make a correction to this article.
» Add information or comments to this article.
Spread the word: del.icio.us del.icio.us it!

See also:

PITCHBLENDE, or URANINITE , a See also:mineral See also:species consisting essentially of See also:uranium See also:oxide, of importance as a source of uranium and See also:radium. It is a very heavy (specific gravity 9.0-9.7), compact mineral with a conchoidal to uneven fracture, and a brownish to See also:velvet-See also:black See also:colour and pitchy lustre. Crystals are rare; they have the See also:form of See also:regular octahedra or less often of cubes. The hardness is 51, and the streak is See also:brown with a greenish tinge. The mineral has been known to occur at Joachimsthal in Bohemia since 1727, and it was See also:early called pitchblende, because of its See also:appearance; but its true nature was not recognized until 1789, when M. H. See also:Klaproth's See also:analysis of it resulted in the See also:discovery of the See also:element uranium. Analyses of material from different localities exhibit wide See also:variations in chemical See also:composition. In addition to uranium oxides, there are See also:thorium, See also:cerium (and lanthanum), See also:yttrium and See also:lead oxides, each varying in amount from a trace up to ro%. See also:Calcium, See also:iron, See also:magnesium, See also:manganese, See also:silica, See also:water, &c., are also See also:present in small amounts. The amounts of uranous and uranio oxides (UO2, 21-72; UO3, 13-59%) also vary considerably. The mineral is often described as a uranate of uranyl; lead, thorium and cerium; but in the least altered material from Branchville in See also:Connecticut the uranous oxide predominates, whilst in altered specimens uranic oxide is in excess.

In the closely allied mineral, See also:

thorianite, thorium predominates (ThO2, 76; UO2i 12 °o). Since the dioxides of uranium, thorium and cerium may be obtained artificially as cubic crystals, it seems probable that pitchblende consists of isomorphous mixtures of these dioxides, the uranic oxide being due to oxidation. The radio-active properties of pitchblende are of See also:special See also:interest. The fact that this mineral is more strongly radio-active than metallic uranium led to the discovery in it of the elements radium, polonium and actinium. When pitchblende is ignited or dissolved in dilute sulphuric See also:acid, a See also:gas is evolved which consists largely of See also:helium and See also:argon: terrestrial helium was first recognized in this mineral. The mineral occurs either as a See also:primary constituent of granitic rocks or as one of secondary origin in metalliferous See also:veins. Octahedral crystals (" cleveite " and " broggerite ") occur in the See also:pegmatite veins of See also:southern See also:Norway, being occasionally found in the See also:felspar quarries at See also:Moss, See also:Arendal and other places. Crystals are found under similar conditions at See also:Middletown and Branchville in Connecticut, Llano See also:county in See also:Texas (" nivenite "), See also:Mitchell county in See also:North Carolina, Villenveuve in See also:Quebec, and other See also:American localities. Thorianite, found as water-worn cubes in the See also:gem-gravels near Balangoda in Sabaragamuwa See also:province, See also:Ceylon, has also no doubt been derived from crystalline rocks. On the other See also:hand, the mineral found in metalliferous veins, and to which the name pitchblende is more properly restricted, never occurs as crystals, but as compact masses rendered more or less impure by admixture of other minerals, the specific gravity being sometimes as See also:low as 6.5; thorium, cerium, &c., are absent, and radium and helium are present in smaller amounts. This variety occurs with ores of See also:silver, lead, See also:copper, See also:nickel, See also:cobalt, See also:bismuth, &c., at Johanngeorgenstadt, See also:Marienberg and See also:Schneeberg in See also:Saxony, Joachimsthal and Przibram in Bohemia, Rezbanya in Bihar Mountains in See also:Hungary, See also:Gilpin county in See also:Colorado, St Just, in Penwith, See also:Redruth, See also:Grampound Road and elsewhere in See also:Cornwall. Often associated with pitchblende, and resulting from its alteration, is an See also:orange-yellow, amorphous, See also:gum-like mineral called gummite, which is a hydrous uranic oxide with small amounts of lead, calcium, iron, &c.

(L. J.

End of Article: PITCHBLENDE, or URANINITE

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.
Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
PITCH, MUSICAL 		[next]
PITCHER

Site © 2006 - Net Industries