About the blog: What Things Are Made Of


The United States relies on imports for dozens of commodities in everyday use. Often enough, that reliance is 100%. In this book I aim to provide awareness of the hidden geology and mineralogy behind common things, and to develop an appreciation for the global resource distribution that underpins our society. While concerns about oil import reliance are in the news every day, our needs for other minerals are comparable and are typically unknown even to technologically aware Americans.

Friday, January 15, 2010

You've got gypsum!

Virtually every home in America contains a great volume of one mineral: gypsum, the primary constituent of wallboard.

Gypsum (chemically, calcium sulfate) crystallizes from supersaturated sea or lake water when the water evaporates, much like common salt precipitates from such water. In the United States, Oklahoma is the leading producer of gypsum—nearly 3,500,000 tons of it, worth more than $26 million in 2007.

But wait, you say — Oklahoma is nowhere near an evaporating sea bed, or even a lake! True, but 255,000,000 years ago, Permian time, as dinosaurs were about to begin their long reign, western Oklahoma was indeed a shallow, restricted lagoon or arm of the sea, and the climate was arid along a shoreline not far from the equator. Evaporation happened.

In Oklahoma’s Blaine Formation four to six gypsum layers, each as much as 10 feet thick, separate thin red shale beds. Shale solidifies from mud, and its red color reflects exposure to the atmosphere as evaporation proceeded: the iron in the mud oxidized to hematite—red iron oxide, essentially rust.

In today’s arid Oklahoma, when groundwater dissolves ancient gypsum and re-deposits it, beautiful crystals form. Oklahoma’s official state crystal is selenite, a type of gypsum found most notably at Great Salt Plains State Park near Jet, a town in northwestern Oklahoma.

After Oklahoma, U.S. gypsum production leaders are Arkansas, Iowa, California, Nevada, Texas, Indiana, and Michigan. But our total, nearly 13 million tons a year, can’t satisfy U.S. wallboard demand. Imports, mostly from Canada, Mexico, and Spain, account for more than 25% of US gypsum consumption. As with so many minerals, China leads the world with gypsum production more than triple that of the United States.

Based on What Things Are Made Of, Chapter 1: All The Ships of the World.

Public domain gypsum image via Wikipedia.


Michael said...

RE: "but several scientific studies found that U.S.-made drywall produced more H2S than the Chinese product."

Please cite these references, which should be a challenge, since they don't exist.

Richard Gibson said...

It appears that the US-made sample that I saw reports on is now believed to have been contaminated by Chinese-made material. I will remove the statement unless I can find better support.