Montmorillonite (inclusions in Quartz)
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Montmorillonite is named after the type locality at the town of Montmorillon, Vienne, Poitou-Charentes region, in western France where it was discovered in 1847.

Discovered in 1847; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(Na,Ca)_0.33(Al,Mg)(Si₄O₁₀)(OH)₂ • n(H₂O)

Hydrated Sodium Calcium Aluminum Magnesium Silicate Hydroxide

Molecular Weight:

549.07 gm

Composition:

Sodium

0.84 %

Na

1.13 %

Na₂O

Calcium

0.73 %

Ca

1.02 %

CaO

Aluminum

9.83 %

Al

18.57 %

Al₂O₃

Silicon

20.46 %

Si

43.77 %

SiO₂

Hydrogen

4.04 %

H

36.09 %

H₂O

Oxygen

64.11 %

O

100.00 %

100.58 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/H.18-20

Nickel-Strunz 10th Ed. ID:

9.EC.40

9 : SILICATES (Germanates)
E : Phyllosilicates
C : Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets

Related to:

Smectite Group. Isostructural with Montmorillonite-Vermiculite Group. Beidellite-Montmorillonite Series. Interstratifies with Chlorite, Muscovite, Illite, Cookeite, Kaolinite.

Members of Group:

Smectite Group: Aliettite, Beidellite, Ferrosaponite, Hectorite, Montmorillonite, Nontronite, Pimelite, Saliotite, Saponite, Sauconite, Stevensite, Swinefordite, Volkonskoite, Yakhontovite, Zincsilite

Varieties:

Alumodeweylite, Askanite, Batrachite, Calcium-Montmorillonite, Delanovite

Synonyms:

Amagorsite, Daunialite, Fuller's Earth, Goumbrine, Gumbrine, Stolpenite, Walkerite (of Dana), Walkthon

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Tiny scaly crystals, tabular on {001}; as lamellar or globular microcrystalline aggregates; clayey, compact, massive. 

Twinning:

None

Physical Properties

Cleavage:

Perfect on {001} 

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

1.0 - 2.0

Density:

2.0 - 3.0 (g/cm³)

Luminescence:

Usually not fluorescent, except by mixtures with Autunite, etc.

Radioactivity:

Not Radioactive

Optical Properties

Color:

White, pale pink, bu®, yellow, red, green; pink to red coloration is due to high valance Manganese (Mn).

Transparency:

Translucent

Luster:

Dull, earthy; low luster due to fine-grained nature of the mineral

Refractive Index:

1.485 - 1.550  Biaxial ( - )

Birefringence:

0.020

Dispersion:

None

Pleochroism:

Visible. X = colorless to pale brown, yellow-green; Y = dark brown to yellow-green, olive-green, pale yellow; Z = brown to olive-green, pale yellow.

Occurances

Geological Setting:

An alteration product of volcanic tuff and ash, forming bentonite beds, and of pegmatite dikes and wall rocks bordering hydrothermal mineral deposits. Forms under alkaline conditions of poor drainage, with Mg, Ca, Na, and K remaining in the soil.

Common Associations:

Cristobalite, Zeolites, Biotite, Quartz, Orthoclase, Dolomite, Amphiboles, Pyroxenes, Olivine, Calcite, Gypsum, Pyrite, Limonite.

Common Impurities:

Fe, K

Type Locality:

Montmorillon, Vienne, Poitou-Charentes, France

Year Discovered:

1847

View mineral photos:

Montmorillonite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Montmorillonite is a member of the Smectite Group of minerals that also includes Volkonskoite. Montmorillonite and Volkonskoite are also considered members of the general mineral group simply called "the clays". The clays typically form microscopic or very small, soft, platy, micaceous crystals. As a mineral specimen, Montmorillonite is usually massive and dull and not very attractive or interesting. However, Montmorillonite as inclusions in Quartz can be very attrractive and interesting. These Montmorillonite inclusions along with Chlorite and other mineral inclusions are often referred to as Garden Quartz, Landscape Quartz or Scenic Quartz because of the interesting forms that resemble growths of moss or underwater garden or forest scenes. Lodolite is another term, or trade name, used for this varity of Quartz with various mineral inclusions. The name Lodolite translates to mud stone from the Spanish word lodo meaning mud or sludge. Teófilo Otoni in the northern part of the Brazilian state of Minas Gerais is one of the most prolific producers of Lodolite Quartz. Depending on the type of minerals, Lodolite inclusions can be found in various shades of green, brown, pink, red, orange, white and even purple. Montmorillonite inclusions tend to be pinks, reds and browns while Chlorite inclusions are mostly shades of green.

Montmorillonite is named after the type locality at the town of Montmorillon, Vienne, Poitou-Charentes region, in western France where it was discovered in 1847. The town of Montmorillon is located on the Gartemp River in the east of La Vienne and dates back to around the end of the eleventh century.

Distribution: A common clay mineral, with numerous localities worldwide. From Montmorillon, Vienne, France. As inclusions in Quartz from Teófilo Otoni, Minas Gerais, Brazil. In the USA, material considered as standards from Bayard and Santa Rita, Grant County, New Mexico; near Chambers, Apache County, Arizona; at Belle Fourche, Butte County, South Dakota; in Wyoming, on the John C. Lane tract, Upton, Weston County, at Clay Spur, near Newcastle, Crook County, and elsewhere. In the Itawamba mine, Itawamba County, and in mines around Polkville, Simpson County, Mississippi; at Strasburg, Shenandoah County, Virginia.
 

  
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