Author’s Note: This part of a weekly series on geology for a class I am taking this semester at BYU-Idaho. This week’s prompt required students to find a mineral in their local area and explain what it is. Other posts from this assignment can be found under the “Geology 111” category.
Featured Image: The Great Salt Lake Desert as seen from Interstate 80 near Wendover, Utah. (Personal photo)
Okay, no, I didn’t go out in nature to find this mineral, but that’s mostly because I didn’t want to drive out to one of the dry lake beds near me when I had this mineral readily available in my cabinet. But I promise, I didn’t pick this mineral because I’m lazy. Ask my wife, I’m way more interested in the dry lake beds in the Great Basin than any normal person should be looking out on a dry, flat, blindingly white plain.
Recently, Alisha and I drove to the Salt Lake area for her cousin’s wedding. This was the second time I had driven across the Salt Flats west of the Great Salt Lake. On our return trip, I noticed a Morton Salt factory just off Interstate 80. I had always kind of wondered where my table salt came from. I had also always assumed that some of it was pulled from the area surrounding the Great Salt Lake. Turns out, at least some of it does come from Utah.
So, what is a mineral? Minerals are hard objects, but are different from rocks in that they are chemically similar throughout the entirety of the object. Rocks are generally made up of several different minerals, all fused together into one object by heat and pressure. Furthermore, minerals are generally inorganic, meaning that (with a few exceptions) minerals don’t come from living things. Because of this, sugar is not a mineral despite looking exactly like salt.
There are plenty of minerals that are white, and not every white mineral that can be found on dry lake beds in the Great Basin is salt. Furthermore, you’re probably not going to find salt in the granulated form found in your cabinet. Also furthermore, there’s more than one kind of salt that naturally occurs in these settings. So how can you tell that table salt is table salt? My first thought is to try to taste it, but tasting dirt doesn’t really appeal to me and that doesn’t sound like a healthy choice.
Table salt, scientifically known as halite, can be identified by the blocky structure that it naturally forms in. If you were to break the halite pictured above, it would break along the margins of the individual cubes. This is because the atomic bonds at the edges of the cubes are significantly weaker than the atomic bonds within the cubes themselves. Using this method to determine if a mineral is halite or not is probably quite a bit safer than licking it.
So how does table salt in my cabinet that might have been sourced from Utah relate to Nevada geology? Like Utah, much of Nevada lies within the Great Basin. Unlike other river systems in the United States where the water flows to the ocean, such as the Columbia and Mississippi systems, not a drop of water from the Great Basin flows to the ocean. Water here generally flows to what are called terminal lakes, where the water leaves by evaporation. Examples of terminal lakes are the Great Salt Lake and Pyramid Lake. Because these lakes have no outlet to the sea, they have varying levels of saltiness. Pyramid Lake near where I live is about 1/6 as salty as the ocean, while the Great Salt Lake can be up to eight times as salty as the ocean depending on its size.
Also like northwestern Utah, many parts of Nevada were once the home to massive inland lakes. As the climate of the region changed and Lake Lahontan dried up, it left behind large playas that contain, among other things, leftover salt. Some of these, like Carson and Humbolt Sinks, become small lakes during spring runoffs and periods of heavy precipitation. Carson Sink is incredibly large, and can be seen from Interstate 80. Other sinks are very small, such as a handful of small ones I’ve found north of Fernley during several Geocaching adventures.
There are numerous terminal dry lakes in the Great Basin, which extends to include portions of Oregon, California, Nevada, Idaho and Utah. On a typical satellite map, you can generally point out these terminal lakes as being a white area surrounded by brown desert. In the map above, I chose not to label dry lake beds in southeast Oregon so you can see them clearly.
My favorite sink to explore is Carson Sink. It is located about 30 miles east of us here in Fernley. Right now the sink contains a lake, but last fall it was bone dry. On the other side of I-80 from Carson Sink are miles of gravel roads that take you around the ghost town of Jessup. There are many abandoned mines around Jessup, so if you decide to go on an adventure out there be aware of them and don’t go in them.