|HALITE FROM DELAWARE BASIN, NEW MEXICO. CUBE ~2.5 X 2.5 CM|
|HALITE CRYSTAL FROM PERMIAN SALT, KANSAS. CUBE ~ 2.5 X 3.0.|
|HALITE CRYSTALS FROM SEARLES LAKE, CALIFORNIA. WIDTH ~9 CM.|
|GOOGLE MAP VIEW OF BIG BASIN, A SINKHOLE LOCATED IN SOUTHWESTERN KANSAS. THE CIRCULAR STRUCTURE IS ABOUT ONE MILE IN DIAMETER. NOTE ROAD DISSECTING THE FEATURE.|
In central Kansas, where I spent my youth wandering hills of the Dakota Formation (Cretaceous), I was fascinated with the amount of halite leaching out of the rocks. The Jamestown Wildlife Refuge is a major stop for migrating waterfowl in the Central Flyway, and a tremendous place to “bird watch”. The refuge is a large marsh with a series of salt water springs and seeps issuing from the upper part of the Dakota. As the water evaporates halite crystals are constantly being produced (and re-dissolved) along water’s edge.I grew up on the Saline River below its contact with the Dakota and the water was highly charged with sodium chloride and could not be used for direct irrigation of plants and crops (several thousand milligrams of chloride per liter). The Saline is a fairly long river at ~400 miles (entirely in Kansas) but is actually quite small in size---except during the numerous floods! There are at least two “Salt Creeks” flowing into the Saline and French explorers noted the “briny” water as early as 1724.
So halite, a somewhat interesting mineral, is similar to many of the other evaporates--they seem rather dull as a collectable mineral. Halite comes in a variety of colors, mostly light in nature, with the tint commonly due to small amounts of impurities. However, at a recent show my eyes about popped out when I discovered a dealer with several specimens of blue to purple halite, a really bright-colored halite! At first I thought perhaps this was simply a crystal constructed from a halite-saturated solution with food coloring added in. But, I was assured the crystal was natural. I had really never seen blue to purple halite before but thought it would look nice in my collection for a couple of dollars. After returning home I begin a literature search to try and locate information about this halite and came across several specimens listed for sale in the 50 to 500 dollar range. That aspect made me feel good about my frugal purchase!
There are some rather famous collecting localities for colored halite in Poland; however, it appears that all blue to purple halite collected in this country comes from potash mines in the Delaware Basin of southeastern New Mexico: the upper Permian McNutt member of the Salado Formation Bickham, (2012). As for origin of the blue to purple color, many/most geologists believe the coloration is due to gamma-ray bombardment of halite with the rays coming from radioactive potassium-40 found in associated minerals (like sylvite: KCl and isomorphous with halite). K-40 is rare but does occur in some instances. The gamma rays then disrupt the lattice structure of the halite and force the displaced electrons to reflect the blue to purple wavelengths from the visible light. I am not enough of a mineralogist to vote yay or nay on this thought but it sounds good to me. Bickham (2012) has some other ideas that seem worth exploring. Whatever the reason for the bright color, these specimens make very nice displays and certainly generate many questions from visitors.
Bickham, M., 201, Chemical Analysis of Blue Halite [abs]: Geological Society of America Abstracts with Programs. V. 44, no. 1.