Roger Weller, geology instructor
Isle Royale in Lake Superior
Pumpellyite is a hydrous calcium aluminum silicate and a member of the zeolite family of
minerals. It is closely related to thomsonite, a hydrous calcium sodium aluminum silicate.
In the following photograph, small growths of thomsonite (pink) are attached to the
pumpellyite (green). These pumpellyite nodules formed in small gas pockets (amygdules)
in a basalt. As the basalt weathered the nodules were freed from the basalt and washed
up on the shores of Isle Royale in Lake Superior. For many years these small nodules went
by the name, chlorastrolite. The largest of these nodules is about 1 centimeter.
Photo is copyright free for non-commercial educational uses.
Just credit photo to R.Weller/Cochise College.