Montmorillonite

Part of speech: noun

Definitions

1. A fine-grained clay mineral belonging to the smectite group, known for its ability to absorb water and expand
2. A naturally occurring clay composed mainly of hydrated aluminum silicate, valued for its swelling and adsorption properties
3. A soft, white to yellowish clay mineral that swells significantly when wet and is used in drilling muds and as an absorbent

Etymology: Montmorillonite takes its name from a small town in western France, Montmorillon, in the department of Vienne. The mineral was identified there, and the name was built by adding the mineral suffix "-ite" to the place name, the same pattern used for many other minerals named after their localities. The suffix is the key to how the word is built. "-ite" comes from Greek "lithos", meaning stone, and is attached to place names, people's names, or descriptive terms to label minerals and rocks. So the word is essentially "the stone of Montmorillon," a label that records where the clay was first found rather than describing what it does. The mineral's name thus says nothing about its famous property. Its tendency to swell dramatically when it absorbs water, which makes it useful in drilling muds and as an absorbent, is a physical trait that the place name does not hint at at all.