The key difference between bentonite and montmorillonite clay is that bentonite is a type of clay consisting mainly of sodium montmorillonite, whereas montmorillonite clay is a type of clay consisting mainly of either sodium or calcium montmorillonite mineral crystals.
Clay is a material with fine-grained natural soil consisting of clay minerals. These are hydrous aluminum phyllosilicates with variable amounts of iron, magnesium, alkali metals, etc. Bentonite and montmorillonite are two types of clay. These are usually distinguished from each other according to their composition. Since both these contain montmorillonite crystals, people usually use these names interchangeably, but they are slightly different from each other.
CONTENTS
1. Overview and Key Difference
2. What is Bentonite Clay
3. What is Montmorillonite Clay
4. Bentonite vs Montmorillonite Clay in Tabular Form
5. Summary – Bentonite vs Montmorillonite Clay
What is Bentonite Clay?
Bentonite clay is an absorbent swelling clay composed mainly of montmorillonite. This can be either sodium montmorillonite or calcium montmorillonite. Among these two types, sodium montmorillonite has a comparatively much higher swelling capacity.
Generally, bentonite tends to form via weathering of volcanic ash in seawater. Sometimes, it forms from hydrothermal circulation with the use of the porosity of volcanic ash beds, which can convert volcanic glass (that can be found in ash) into clay minerals. Moreover, this mineral alteration process has a large portion of amorphous silica that is dissolved and leached away. This can lead to the presence of bentonite deposits in different places.
Typically, a bentonite bed appears in white or pale blue, or green when it is freshly exposed. However, this turns into a cream color or yellow (later into red or brown) upon exposure to further weathering.
Since bentonite is a swelling clay that can absorb large quantities of water, it can increase the volume of the clay up to a factor of eight. This can make bentonite bends highly unstable to be used as a building material and for road construction. Nevertheless, this swelling property can be useful in the drilling mud and groundwater sealants.
What is Montmorillonite Clay?
Montmorillonite clay is a type of phyllosilicate mineral that can form upon the precipitation from water solution in the form of microscopic crystals known as clay. This material was named after Montmorillon in France. It has a monoclinic crystal system, and it belongs to the prismatic 2/m crystal class. The space group of this substance is C2/m.
The appearance of montmorillonite clay can be described as white, pale pink, blue, yellow, red, or green color. When considering its crystal habit, montmorillonite clay shows compact masses of lamellar or globular microcrystalline aggregates, and the cleavage can be described as “perfect.” The fracture of montmorillonite is uneven, and the luster is dull or earthy. It appears translucent, and the specific gravity is in the range of 2 – 3. The hardness of this clay material can be given in the 1-2 range.
What is the Difference Between Bentonite and Montmorillonite Clay?
Bentonite and montmorillonite are two important types of clay materials. The key difference between bentonite and montmorillonite clay is that bentonite is a clay material consisting mainly of sodium montmorillonite, whereas montmorillonite clay is a type of clay consisting mainly of either sodium or calcium montmorillonite mineral crystals.
Below is a summary of the difference between bentonite and montmorillonite clay in tabular form for side-by-side comparison.
Summary – Bentonite vs Montmorillonite Clay
Both bentonite and montmorillonite clay contain montmorillonite crystals. However, there is a difference between bentonite and montmorillonite clay in terms of their composition. Bentonite is a clay material consisting mainly of sodium montmorillonite, whereas montmorillonite clay is a type of clay consisting mainly of either sodium or calcium montmorillonite mineral crystals.
Reference:
1. “Clay.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.
Image Courtesy:
1. “Gray shale & bentonites (Benton Shale, Upper Cretaceous; Red Rock Canyon Open Space, Colorado Springs, Colorado, USA) 4” By James St. John – (CC BY 2.0) via Commons Wikimedia
2. “Montmorillonite-Quartz-pala48a” By Rob Lavinsky, iRocks.com – (CC BY-SA 3.0) via Commons Wikimedia