This earth cache highlights the formation and deposits of pumice. Please note that the mining operations go right up the to public road. There is no need to (and please don't) enter the pit or disturb their operations. The road here is maintained year round but extra care should be taken in the winter as it is remote and the road leading here is narrow and winding. The last little bit is gravel but the family car should make it just fine. Don't count on cell service either.
Pumice Formation
Deep inside an ancient volcano, water mixed with molten rock building pressure until finally erupting a violent, spectacular release. The water that was trapped in the viscous, super-heated rock flashed to steam changing the magma into a frothy stone as it is rapidly cooled and depressurized. It then hardens and falls to the earth as pumice.
This pumice deposit is located on the shoreline of ancient Lake Bonneville, a vast, freshwater lake that once covered much of the Great Basin region (most of Utah and parts of Idaho and Nevada). Lake Bonneville existed in the area from 30,000 years ago to about 13,000 years ago. It was during this time this deposit was created. The Great Salt Lake is all that remains of Lake Bonneville.
The volcano that produced the pumice is about a mile to the north of the mine. The volcanic ash (pumice) was deposited in the lake, where it was washed and stratified. This process cleaned the pumice of the undesirable heavy minerals that are often found in other pumice deposits.
Pumice Properties
Pumice is a foamed-glass stone that is hard yet friable (easily pulverized), amorphous (lacking crystal formation due to it's cooling very rapidly) in structure, naturally calcined (process of heating to revome impurities) and highly vesicular (pitted with many cavities or visicles on it's surface and inside) rough textured
On the Mohs hardness scale, pumice has of value of 6, where 1 (talc) is the softest and 10 (diamond) is the hardest. With a value of 6, it cannot be scratched by a knife but it can scratch glass. A hardness of this value, allows pumice to maintain it's vesicular nature when pulverized.
Not all pumice is created equally. It can vary greatly in its chemical properties (and usefulness) from deposit to deposit, but essentially, pumice is primarily Silicon Dioxide (Amorphous Aluminum Silicate), some Aluminum Oxide, and trace amounts of other oxides.
The abundant vesicles in pumice and the thin walls between them give the rock a very low specific gravity. It typically has a specific gravity of less than one, giving the rock an ability to float on water.
Pumice Uses
The value of pumice to infrastructure and industry goes back at least 2000 years. Roman engineers knew that by adding fine-grained pumice, or “pozzolana” to their hydrated lime cement, the result was a strong, durable concrete. Some two millennia later, much of their empire of concrete—roads, aqueducts, temples, stadiums, piers—still stands defiantly against the ravages of time. Today, pumice powder is still being used as a superior pozzolan to super-charge concrete strength and durability, but is also used widely in a variety of industrial processes and product applications.
The largest use of pumice in the United States is the production of lightweight concrete blocks and other lightweight concrete products. When this concrete is mixed, the vesicles remain partially filled with air which reduces the weight of the block. Lighter blocks can reduce the structural steel requirements of a building or reduce the foundation requirements. The trapped air also gives the blocks a greater insulating value.
The second most common use of pumice is in landscaping and horticulture. The pumice is used as a decorative ground cover in landscaping and planters. It is used as drainage rock and soil conditioner in plantings
Other minor uses of pumice include its use as an abrasive in soaps, pencil erasers, and polishes. It can also be used as traction enhancers on roadways and tires.
Logging requirements
In order to log this earth cache please send me an email or message through geocaching.com within 2 days of your log with answers to the following questions.
1. Based on your observation at posted coords and above description, why do you think the pumice has been deposited here in this location?
2. One of the uses of pumice is in cosmetics as an exfoliant. What properties of pumice do you think make it good for that use?
3. Please post in your log a picture of you or a personal item at posted coords with the deposit in the back ground.
Sources
https://hesspumice.com/pumice-pages/why-pumice/pumice-defined.html
http://aboutpumice.com/pumice-info.html
https://en.m.wikipedia.org/wiki/Pumice
https://geology.com/rocks/pumice.shtml
https://www.rocksandminerals4u.com/pumice.html