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The Mineral Leucite

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The Mineral Leucite Definition of LEUCITE :: a white or gray mineral consisting of a silicate of potassium and aluminum and occurring in igneous rocks THE MINERAL LEUCITE Chemistry: KAlSi22OO66, Potassium Aluminum Silicate Class: Silicates Subclass: Tektosilicates Group: Feldspathoids Uses: mineral specimen and as a minor source of potassium and aluminum. Specimens Leucite is a popular and interesting mineral. Its name comes from the greek word for "white" in allusion to its typical color. At high temperatures, leucite is isometric and will form the isometric trapezohedron crystal form. Interestingly, as leucite cools, the isometric structure becomes unstable and transforms into a tetragonal structure without altering the outward shape. Although the mineral is actually tetragonal, the outward shape is pseudo- isometric and thus the crystal form is actually pseudo- trapezohedral. Leucite is one of the few minerals that forms the unique trapezohedron. The trapezohedron has 24 deltoid shaped faces, where each face occupies one third of the position of a single octahedron's face. The minerals of the garnet group and the mineral analcime are the only common minerals that will also form the trapezohedron. Distinguishing leucite from the garnets and analcime is relatively easy in some cases. The garnets are much harder and usually deeply colored. Leucite has a much lower density and usually has a duller luster than analcime. Also leucite is typically embedded in host rock where as analcime, when displaying good crystals and not massive or granular, is loose or attacted to other minerals in volcanic cavities. Leucite, KAlSi22OO66 is actually distantly related to analcime, NaAlSi22OO66-H22O. Leucite is a member of the feldspathoid group of minerals. Analcime, although usually considered a zeolite, is sometimes placed in the feldspathoid group since its chemistry and occassional occurrences are similar. Minerals whose chemistries are close to that of the alkali feldspars but are poor in silica (SiO22) content, are called feldspathoids. Leucite, like other feldspathoids, is found in silica poor rocks containing other silica poor minerals and no quartz.. If quartz were present when the melt was crystallizing, it would react with any feldspathoids and form a feldspar.. At one time leucite was used as a source of potassium and aluminum. Probably due to the high aluminum to silicon ratio, its structure is easily destroyed by acids and this frees the aluminum ions. Leucite, already a pseudomorph from a high temperature phase, commonly is altered to pseudoleucite. Pseudoleucite is not a mineral but a mixture of nepheline,, orthoclaseand analcime. PHYSICAL CHARACTERISTICS: Color is clear, white or gray, with yellowish and reddish tints possible. Luster is vitreous or greasy to dull. Transparency: crystals are transparent, translucent to commonly opaque. Crystal System is isometric; 4/m bar 3 2/m at temperatures above 605 degrees C, and tetragonal; either 4 2 2 or 4/m, below 605 degrees C. Crystal Habits include the characteristic trapezohedron (actually pseudo-trapezohedron). Also granular and massive. Cleavage is absent. Fracture is conchoidal Hardness is 5.5 - 6. Specific Gravity is approximately 2.4 - 2.5 (slightly below average) Streak is white. Associated Minerals include olivine, labradorite, augite, biotite, neph eline and other feldspathoids. Other Characteristics: surface is usually pitted, dull or has a weathered look. Notable Occurrences include Mt. Vesuvius, Italy; Magnet Cove, Arkansas, Leucite Hills, Wyoming and Litchfield, Maine, USA; Brazil and Hastings Co, Ontario. Best Field Indicators are crystal habit, density, low hardness, luster and associations. http://www.galleries.com/Leucite http://www.mindat.org/min-2465.html General Leucite Information Chemical Formula: KAlSi2O6 Composition: Molecular Weight = 218.25 gm Potassium 17.91 % K 21.58 % K2O Aluminum 12.36 % Al 23.36 % Al2O3 Silicon 25.74 % Si 55.06 % SiO2 Oxygen 43.99 % O ______ ______ 100.00 % 100.00 % = TOTAL OXIDE Empirical Formula: KAl(Si2O6) Environment: Acid volcanic rocks. IMA Status: Valid Species (Pre-IMA) 1791 Locality: Bearpaw Mountains., Montana, USA. Link to MinDat.org Location Data. Name Origin: From the Greek leukos - "white." Name Pronunciation: Leucite Synonym: Amphigene Leucite Image Images: Leucite Comments: Large single crystal of dark gray leucite. Location: Roccamonfina, Caserta Province, Campania, Italy. Scale: 20x20x20 mm. © John Betts - Fine Minerals Leucite Crystallography Axial Ratios: a:c = 1:1.05042 Mineral News Wrights Rock Shop Translate Leucite Mineral Data : Ask about Leucite here : Ask-A-Mineralogist from the Mineralogical Society of America Mindat.org's Discussion Groups Original Rockhounds Discussion Group Rockhounds Discussion Group on Yahoo Groups Mineral Discussion Forum from Fabre Minerals - also available in Español Print or Cut-and-Paste your Leucite Specimen Label here : Leucite KAlSi2O6 Dana No: 76.02.02.01 Strunz No: 09.GB.05 Locality: Notes: http://webmineral.com/data/Leucite.shtml Leucite : K(AlSi2O6) Stradner Kogel, Wilhelmsdorf, Bad Gleichenberg, Styria, Austria Grey Leucite-xl; + Apatite(white needles), Diopside(green -"-); Picture width: ~10mm; Field collected /by: 2003/ReMi; Collection/photo: ReMi/ReMi © ReMi Photo ID: 73509 View Count: 504 Leucite : K(AlSi2O6) Cascata, guas da Prata, São Paulo, Brazil single leucite crystal. Size 2x1,5x1cm. Rafael Hernandes Corrêa-Silva © Brhounds Photo ID: 45120 View Count: 498 Leucite : K(AlSi2O6) Krušné Hory Mts (Erzgebirge), Karlovy Vary Region, Bohemia (Böhme A 4cm single leucite crystal. Photo is made in 2005. © 2005 S.Sayamov Photo ID: 34471 View Count: 693 Leucite : K(AlSi2O6) Radešin Hill, Ústí nad Labem (Aussig), Ústí Region, Bohemia (Böhmen Field of view 5mm © Petr Fuchs Photo ID: 65207 View Count: 442 Leucite : K(AlSi2O6) Radešin Hill, Ústí nad Labem (Aussig), Ústí Region, Bohemia (Böhmen FOV 3mm © Petr Fuchs Photo ID: 134600 View Count: 292 Leucite : K(AlSi2O6) Lapanouse-de-Sévérac (slag locality), Aveyron, Midi-Pyrénées, France Field of wiew: 1,5mm Collection & Photo: D.Journet © D.JOURNET Photo ID: 340881 View Count: 163 Leucite : K(AlSi2O6) .
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