Laumontite
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Laumontite was originally named Laumonite in 1805 by German geologist Abraham Gottlieb Werner (1749-1817) in honor of French mineralogist François Pierre Nicolas Gillet Laumont (1747-1834), Inspector General of Mines, who discovered the mineral.

Discovered in 1805; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

CaAl₂Si₄O₁₂ • 4(H₂O)

Hydrated Calcium Aluminum Silicate

Molecular Weight:

470.44 gm

Composition:

Calcium

8.52 %

Ca

11.92 %

CaO

Aluminum

11.47 %

Al

21.67 %

Al₂O₃

Silicon

23.88 %

Si

51.09 %

SiO₂

Hydrogen

1.71 %

H

15.32 %

H₂O

Oxygen

54.42 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/J.22-50

Nickel-Strunz 10th Ed. ID:

9.GB.10

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

Related to:

Zeolite Group. Laumontite Subgroup.

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:

Caporcianite, Leonhardite, Vanadio-laumontite

Synonyms:

Aedelforsite, ICSD 72914, Laumonite, Lomonite, PDF 45-1325, Schneiderite

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals square prisms with steep oblique terminations, stout, commonly elongated, to 20 cm. Radiating, columnar, fibrous; in interlocking aggregates, massive.

Twinning:

On {100}, typically with terminal re-entrants. 

Physical Properties

Cleavage:

Perfect on {010}, {110}

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

3.0 - 4.0 

Density:

2.23 - 2.41 (g/cm³)

Luminescence:

Fluorescent; weak white under SW and LW UV

Radioactivity:

Not Radioactive

Other:

Undergoes a partial loss of H2O on exposure to air.

Optical Properties

Color:

White to gray, pink, yellowish, brownish, golden brown; colorless in thin section.

Transparency:

Transparent to translucent

Luster:

Vitreous to pearly on cleavages

Refractive Index:

1.502 - 1.526  Biaxial ( - )

Birefringence:

0.007 - 0.012

Dispersion:

Distinct; r < v;  weakly inclined.

Pleochroism:

None

Occurances

Geological Setting:

Of hydrothermal origin, lining cavities in igneous rocks. Thick sedimentary beds rich in laumontite may form by decomposition of analcime or metamorphism of plagioclase. May be authigenic, cementing sandstones.

Common Associations:

Zeolites, Apophyllite, Datolite, Calcite, Chlorite

Common Impurities:

Na, K, Fe

Type Locality:

Huelgoat (Locmaria-Berrien), Finistère, Brittany, France

Year Discovered:

1805

View mineral photos:

Laumontite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Laumontite is a member of the Zeolite Group of minerals that also includes Analcime, Barrerite, Chabazite, Epistilbite, Gmelinite, Goosecreekite, Heulandite, Leucite, Mordenite, Natrolite, Pollucite, Scolecite, Stellerite, Stilbite, Thomsonite and Yugawaralite. Laumonite is a "hydrated" mineral, meaning it contains water. Unfortunately, this means that exposure to air causes it to lose some of its water which can destabilize crystals or gems and cause them to become powdery. When this happens, Laumontite dehydrates to become a different mineral called Leonhardite. Leonhardite is the name for partially dehydrated, opaque Laumontite. Laumontite crystals and gems should be sealed in an air tight container for storage. Fortunately, the dehydration alteration is slow and a specimen or gem can remain in good condition for many years if it is cared for properly.

Leonhardite was named by Johann Reinhard Blum (1802-1883) in 1843 in honor of Karl Ritter von Caesar Leonhard (1779-1862). Von Leonard was a tax assessor and administrator of the Grand Duchy of Frankfurt, and eventually, he became Professor of mineralogy at the University of Heidelberg, Germany.

Laumontite was originally named Laumonite (missing a "t") in 1805 by Abraham Gottlieb Werner (1749-1817) in honor of François Pierre Nicolas Gillet Laumont (1747-1834), Inspector General of Mines, who discovered the mineral. The name was changed to its current spelling, Laumontite, in 1821 by Karl Ritter von Caesar Leonhard. Laumont's birth name was François Pierre Nicolas Gillet. He took on the name "of Laumont" to distinguish himself from his older brother François Pierre Gillet of Renommière (1734-1813). Perhaps the mineral should have been named Gilletite.

Laumontite distribution: relatively common. Well-crystallized specimens: from Huelgoat, Finistμere, France. From Sãcãrâmb (Nagyág), Romania. At St. Gotthard, Ticino, Switzerland. From Floitental, Zillertal, and other places in Tirol, Austria. In Italy, from Baveno, Piedmont. From Poona and in the Khandivali quarry, near Bombay, Maharashtra, India, large crystals. In the USA, exceptional crystals from the Pine Creek tungsten mine, Bishop, Inyo County, California; from Drain, Douglas County, Oregon; at Bergen Hill, Hudson County, and Paterson, Passaic County, New Jersey; in the Goose Creek quarry, Leesburg, Loudoun County, Virginia; on the Keweenaw Peninsula, Houghton and Keweenaw Counties., Michigan.
 

  
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