Online Encyclopedia

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

GALENA

Online Encyclopedia
Originally appearing in Volume V11, Page 400 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!

GALENA , an important ore of See also:

lead, consisting of lead sulphide (See also:PbS). The See also:mineral was mentioned by See also:Pliny under this name, and it is sometimes now known as lead-glance (Ger. Bleiglanz). It crystallizes in the cubic See also:system, and well-See also:developed crystals are of See also:common occurrence; the usual See also:form is the See also:cube or the cubo-See also:octahedron (fig.). An important See also:character, and one by which the mineral may always be recognized, is the perfect cubical cleavage, on which the lustre is brilliant and metallic. The See also:colour of the mineral and of its streak is lead-See also:grey; it is opaque; the hardness is 21 and the specific gravity 7.5. Twinned crystals are not common, but the presence of polysynthetic twinning is sometimes shown by See also:fine striations See also:running diagonally or obliquely across the cleavage surfaces. Large masses with a coarse or fine granular structure are of common occurrence; the fractured surfaces of such masses See also:present a spangled See also:appearance owing to the numerous See also:bright cleavages. The See also:formula PbS corresponds with lead 86.6 and See also:sulphur 13.4%. The mineral nearly always contains a small amount of See also:silver, and sometimes See also:antimony, See also:arsenic, See also:copper, See also:gold, See also:selenium, &c. Argentiferous galena is an important source of silver; this See also:metal is present in amounts rarely exceeding 1 %, and often less than 0.03 % (See also:equivalent to ro4 ounces per ton). Since See also:argentite (Ag2S) is isomorphous with galena, it is probable that the silver isomorphously replaces lead, but it is to be noted that native silver has been detected as an enclosure in galena.

Galena is of wide See also:

distribution, and occurs usually in metalliferous See also:veins traversing crystalline rocks, See also:clay-slates and See also:lime-stones, and also as pockets in limestones. It is often associated with See also:blende and See also:pyrites, and with See also:calcite, fluorspar, See also:quartz, See also:barytes, See also:chalybite and pearlspar as See also:gangue minerals; in the upper oxidized parts of the deposits, See also:cerussite and anglesite occur as alteration products. The mineral has occasionally been observed as a See also:recent formation replacing organic See also:matter; such as See also:wood; and it is sometimes found in beds of See also:coal. As small concretionary nodules, it occurs disseminated through See also:sand-See also:stone at Kommern in the See also:Eifel. In the lead-See also:mining districts of See also:Derbyshire and the See also:north of See also:England the ore occurs as veins and flats in the Carboniferous See also:Limestone See also:series, whilst in See also:Cornwall the veins See also:traverse clay-slates. In the Upper See also:Mississippi lead region of See also:Missouri, See also:Illinois, See also:Iowa and See also:Wisconsin the ore fills large cavities or See also:chambers in limestone. Galena is met with at all places where lead is See also:mined; of localities which have yielded finely crystallized specimens the following may be selected for mention: Derbyshire, See also:Alston in See also:Cumberland, Laxey in the Isle of See also:Man (where crystals measuring almost a See also:foot across have been found), Neudorf in the Harz, Rossie in New See also:York and See also:Joplin in Missouri. See also:Good crystals have also been obtained as a See also:furnace product. Coarsely grained galena is used for See also:glazing pottery, and is then known as " potters' ore " or alquifoux. The galena See also:group includes several other cubic minerals, such as argentite (q.v.). Mention may also be made here of clausthalite (lead selenide, PbSe) and altaite (lead telluride, PbTe), which, with their lead-grey colour and perfect cubic cleavage, closely resemble galena in appearance; these See also:species are named after the localities at which they were originally found, namely, Klausthal in the Harz and the See also:Altai mountains in See also:Asiatic See also:Russia. Altaite is of See also:interest as being one of the tellurides found associated with gold.

(L. J.

End of Article: GALENA

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]
GALEN, CHRISTOPH BERNHARD, FREIHERR VON (16o6-1678)... 		[next]
GALEOPITHECUS

Site © 2006 - Net Industries