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This earthcache features a large historical building made from sandstone quarried near Fort Collins, Colorado.
****I am asking all visitors to provide answers to a few easy questions to ensure you visited the site. Please read and answer carefully.****
Sandstone forms where sand is laid down and buried—beaches, dunes and seafloors. When sand is deeply buried, the pressure of burial and slightly higher temperatures allow minerals to dissolve or deform and become mobile. The grains become more tightly knit together, and the sediments are squeezed into a smaller volume. This is the time when cementing material moves into the sediment, carried there by fluids charged with dissolved minerals. Oxidizing conditions lead to red colors from iron oxides, while reducing conditions lead to darker and grayer colors.
Sandstone is a category of rock made from sediment (a sedimentary rock). The sediment particles are clasts, or pieces, of minerals and fragments of rock, thus sandstone is a clastic sedimentary rock. It is composed mostly of sand, which means particles of a medium size, so sandstone is a medium-grained clastic sedimentary rock. More precisely, sand is between 1/16 millimeter and 2 mm in size (silt is finer and gravel is coarser). Sandstone may include finer and coarser material and still be called sandstone, but if it includes more than 30 percent grains of gravel, cobble or boulder size it's classified instead as conglomerate or breccia (together these are called rudites).
Sandstone has two different kinds of material in it besides the sediment particles: matrix and cement. Matrix is the fine-grained stuff (silt and clay size) that was in the sediment along with the sand whereas cement is the mineral matter, introduced later, that binds the sediment into rock.
The Color Wheel of Sandstone
Sandstone offers a rich palette of crimson, vermilion, orange, salmon, peach, pink, gold, yellow, and white.
The red color is caused by a union of iron and oxygen (an iron oxide) known as hematite (Fe2O3), a mineral named from the Greek word for blood. Iron is a powerful pigment present in many sediments and rocks, thus it commonly imparts color to the rocks.
What happened to make normally red sandstone white?
Sandstone is porous and permeable because there are holes or spaces between sand grains. Sand dunes make particularly permeable sandstone because wind effectively sorts the grains to create a homogeneous deposit with uniform grain size and not much fine-grained pore fillings. Given enough pressure and force, water moves relatively easily through porous sandstone- almost like water through a sponge. Even during heavy rains with much surface runoff, some water infiltrates the sandstone. Under certain conditions, iron pigment will dissolve in water and be removed, or be rendered colorless by chemical reactions with the water. This
is much like a bleaching detergent permeating a red cloth, removing
color as it spreads. (However, household chlorine bleach won’t take out
iron rust stains because chlorine is not chemically able to move iron).
How does bleaching happen chemically? Some waters contain reducing agents (electrons are added to the iron atom and oxygen is removed) that make the iron soluble (dissolvable) in water. To make iron
soluble, the water can restore one of the electrons that was lost by iron during early weathering and oxidation. Fluids such as hydrocarbons (petroleum), weak acids (vinegar-like), or those with hydrogen sulfide
(gas that smells like rotten eggs) can also restore an electron to iron, thus these are called reducing waters. This water can dissolve and remove nearly all of the hematite and bleach red sandstone to white.
To log this earthcache, you must answer these questions:
1. There were 1-5 colors of sandstone used to make this building. How many colors were actually used, and how was each color caused (created) ?
2. What is the date that this building was erected? Include month, day, and year. This info can be found on a stone on the building (outside).
3. What is the altitude where you are standing? Look at the information carved into the stone. This is the Elevation I am looking for...not the elevation on your GPS'r.
Optional: Take a photo of your gps and/or yourself with the Plains hotel just north of this site, or any artowrk near this site in the background. Why? To ensure you actually visited the site. Please do not post spoiler pictures in the cache page.
Thanks!
Additional Hints
(Decrypt)
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