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Why Does Some Sandstone Have Stripes?
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Sandstone sample from Petra |
Once you've made mashed potatoes, could you turn them back into whole potatoes? After you've scrambled eggs, could you separate the yolks and whites, restore them to their original form and put the eggs back into their shells? Maybe not, but here's a story about natural phenomena in geology called Stratification & Segregation that achieve something similar. These phenomena are responsible for the layers we see in some types of sedimentary rocks.
How is sandstone formed?
In Petra, a 2000 year old city in the Jordanian desert, many of the ancient buildings were built and carved out of the local sandstone. As in Petra, sandstone can often be found in areas where windblown sand accumulates over thousands or millions of years. Sand deposits also build up on the ocean floor, or in lakes and rivers. When the sand particles, mixed with cement-like minerals such as quartz and calcite, are compressed under great pressure over long periods of time they stick together to become stone.
accumulated sand + cementing minerals + pressure + time = sandstone
Buildings in Petra were carved out of the local sandstone. |
