Smectite is a mineral, but a mineral with distinct chemical properties. Structural changes in minerals may require millions of years of aging to complete, but a chemical reaction may be completed in only 4 to 5 rain.
Some of the problems of smectite seals are described in this paper, together with methods of avoiding these hazards.
~TRODUCTION
Geologists tell us that most smectites are derived from volcanic ash --fine grained chilled lava belched into the atmosphere~luring an era roughly 70 million years ago. We had a sample of the spread of volcanic ash within the past few years: Mount St. Helens' cloud traversing the world in just a few weeks. It is possible to visualize the dust cover when volcanoes from Alaska down to the Yucatan were all active at approximately the same time.
Unaltered volcanic ash is harsh and gritty --an abrasive. Part of the volcanic ash fell into water. Some geologists believe the ash dissolved, formed a silicate and recrystallized as smectite. Other geologists present a picture of a crystal forming, with part of the crystal leaching away and being replaced by ions in the water.
Blistering hot water was probably needed to dissolve the ash. It is probable that the hot water was available. Portions of Wyoming and Montana known now for extreme cold during winter --minus 40 ยฐ C --are also the source of fossilized tropical ferns, from their jungle vegetation era.
Volcanic ash that deposited in salty water such as the Cretaceous Sea would decay into a sodium smectite with unique properties. Similarly, volcanic ash that settled in fresh water, or was transported into a fresh water area, would become a calcium smectite with vastly different properties. There was a third class of smectite, a mixed calcium--sodium mineral that may have matured in brackish water; it may have been a sodium smectite that was leached with a calcium salt after conversion.