Leucite
Current inventory:  1 gem
 

  
Leucite is named from the Greek word leukos meaning white in allusion to its common color.

Discovered in 1791; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

KAlSi₂O₆

Potassium Aluminum Silicate

Molecular Weight:

218.25 gm

Composition:

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

Classification

Mineral Classification:

SILICATES (Germanates)

Strunz 8th Ed. ID:

8/J.05-10

Nickel-Strunz 10th Ed. ID:

9.GB.05

9 : SILICATES (Germanates)
G : Tektosilicates with zeolitic H₂O; zeolite family
B : Chains of single connected 4-membered rings

Related to:

Zeolite Group.

Members of Group:

Zeolite Group: Alflarsenite, Amicite, Ammonioleucite, Analcime, Barrerite, Beaumontite (of Lévy), Bellbergite, Bikitaite, Boggsite, Brewsterite, Chabazite, Chabazite-Lévyne Subgroup, Chiavennite, Clinoptilolite, Cowlesite, Dachiardite, Direnzoite, Edingtonite, Epistilbite, Erionite, Faujasite Subgroup, Ferrierite, Ferrochiavennite, Flörkeite, Garronite, Gaultite, Gismondine, Gmelinite, Gobbinsite, Gonnardite, Goosecreekite, Gottardite, Harmotome, Heulandite, Hsianghualite, Kirchhoffite, Laumontite, Leucite, Lévyne, Lovdarite, Maricopaite, Mazzite, Merlinoite, Montesommaite, Mordenite, Mutinaite, Nabesite, Natrolite, Offretite, Pahasapaite, Paranatrolite, Parthéite, Paulingite, Perlialite, Phillipsite, Pollucite, Roggianite, Scolecite, Stellerite, Stilbite, Strontiohurlbutite, Terranovaite, Thomsonite, Tschernichite, Tschörtnerite, Wairakite, Weinebeneite, Wenkite, Willhendersonite, Yugawaralite

Varieties:

Germanate-leucite

Synonyms:

Leukolith, Oeil de perdrix, White Garnet

Crystal Data

Crystallography:

Tetragonal - Dipyramidal

Crystal Habit:

Commonly euhedral, pseudocubic crystals, to 9 cm, typically showing fine twin striae. As disseminated grains; rarely granular, massive.

Twinning:

Common and repeated on [110], [101], and other orientations, from two complex displacive phase transformations during cooling.

Physical Properties

Cleavage:

Indistinct; very poor on {110} 

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.0

Density:

2.45 - 2.50 (g/cm³)

Luminescence:

None

Radioactivity:

Barely Detectable; GRapi = 255.81 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

White, gray; colorless in thin section. Yellowish and reddish tints possible due to impurities.

Transparency:

Transparent to Translucent, Opaque

Luster:

Vitreous

Refractive Index:

1.508 - 1.509  Uniaxial ( + ); may be anomalously Biaxial

Birefringence:

0.001

Dispersion:

Moderate

Pleochroism:

None

Occurances

Geological Setting:

With potassium-rich mafic and ultramafic lavas and hypabyssal rocks, and may almost entirely compose them.

Common Associations:

Potassic Feldspar, Nepheline, Analcime, Natrolite, Kalsilite.

Common Impurities:

Ti, Fe, Mg, Ca, Ba, Na, Rb, Cs, H₂O

Type Locality:

Monte Somma, Somma-Vesuvius Complex, Naples Province, Campania, Italy

Year Discovered:

1791

View mineral photos:

Leucite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Leucite is a member of the Feldspathoid Group of minerals that includes Cancrinite, Haüyne, Lazurite, Leucite, Nepheline and Sodalite. Minerals with chemistries that are close to those of the alkalai Feldspars, but are poor in silica (SiO2) content, are called Feldspathoids. Leucite is abundant in various lava rocks but is extemely rare in facetable crystals. Gems are usually small and cloudy or included. The main source of transparent Leucite crystals large enough for faceting is the Alban Hills, near Rome, Italy.

The are numerous localities worldwide. Especially from Italy, as at Vesuvius, Monte Somma, and Roccamonfina, Campania; at Villa Senni, Frascati, and Ariccia, Lazio; and on Vulcano, Lipari Islands. Around the Laacher See, Eifel district, Germany. In the USA, from the Leucite Hills, Sweetwater County, Wyoming; the Bear Paw Mountains, Hill County, Montana; and at Magnet Cove, Hot Spring County, Arkansas. In the West Kimberley district, Western Australia. In Tanzania, on Kilimanjaro. In Uganda, found around Ruwenzori and Kariya. From Mt. Nyiragongo, Kivu Province, Congo (Zaire).
 

  
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