Montmorillonite
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.
| 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 |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Tiny scaly crystals, tabular on {001}; as lamellar or globular microcrystalline aggregates; clayey, compact, massive. |
| Twinning: | None |
| 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 |
| 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. | |
