Calvin College - GGES Department - Field Trip

Field Trips
Geology 151, Gypsum Mine, Grand Rapids

Every semester, students taking introductory geology courses at Calvin College are taken to a gypsum mine 80 feet beneath Grand Rapids. Although the mine used to be open for elementary and highschool age groups, access is now limited to college classes. Below are some photographs from a trip with Steve Schrimmrich on Tuesday, November 17, 1998. The quality of the images is not great--it's difficult to take photos in the dim lighting conditions of the mine!

The geology of this mine is interesting. During the late Mississippian Period of geologic time (some 330 million years ago), this area of Michigan was covered with shallow marine seas which deposited the Michigan Formation consisting primarily of shales, gypsum, and limestones. During this time, North America was much closer to the equator (due to plate tectonic movement of the continents) and this sea was confined to a basin with restricted circulation and high evaporation rates. Sedimentary features like mud cracks and ripple marks in the shales imply that the original sediments were periodically exposed to the air and plant fossils may be found as well.

Evaporating seawater left behind thick deposits of the mineral gypsum which was mined beneath Grand Rapids in the early part of this century (gypsum's primary uses are for gypsum wallboard and plaster of Paris). In the early days, the mining was done by hand with horses pulling carts on rail tracks to the elevators. Gypsum mining was discontinued here in the mid-1940's since it was no longer economical and this mine has been used since as a storage facility by Michigan Natural Storage.

Trivia question: Is gypsum mentioned in the Bible? I've given the answer below.

To enter the mine, we park the vans, walk into a warehouse, and take a short freight elevator ride down to the tunnels

There's a foot-thick shale layer between the gypsum walls and the ceiling of the tunnels. The contact between the gypsum and the shale is irregular implying an ancient erosional surface.

Another view of the irregular contact between the underlying gypsum and the overlying shale at the top of the tunnel walls (the red hose is hanging from the ceiling).

Mud cracks in the ceiling of the tunnels. What do these tell us about the environment in this part of Michigan during the late Mississippian Period?

Ripple marks in the ceiling (easier to see in person). These form in shallow water.

Examining some of the sedimentary structures observed in the tunnel walls and ceilings

Here's what it looks like behind us. There are over six miles worth of tunnels down here, most of which are not lit.

Close-up of clear selenite gypsum veins within the massive orange gypsum comprising the walls of the tunnels (nickel for scale).

We then moved into the unlighted tunnels with our flashlights and explored a bit. I have no pictures of this since it was quite dark! Here are some fragile, fibrous selenite gypsum needles growing in the dark tunnels and illuminated by flashlight (nickel for scale).

A tunnel wall swiss-cheesed with holes. Gypsum is quite soft (you can scratch it with your fingernail) and easily mined in the manner shown here.

Back on the surface and back to the vans.

Answer to the trivia question: Yes, gypsum is mentioned in the Bible but with the word alabaster which denotes a fine-grained variety of gypsum that is often carved into various objects. Matthew 26:7, Mark 14:3, and Luke 7:37 all recount the story of the woman in Bethany who annointed Jesus with expensive perfume from an alabaster jar.