We started with a recap on what we have recently learnt. Then, we went on to the size of the Sediments. Turns out gravel are the biggest, then sand, silt and lastly, clay, which is so teeny weeny small that we can’t see them with our naked eye. As we spent only a little time on this part, I did some research and I found a website that states all these. Here is a paragraph below, taken from
Sediment and Sedimentation - Sediment Size :
“Sediments come in all shapes and sizes. Sediment sizes are classified by separating them into a number of groups, based on metric measurements, and naming them using common terms and size modifiers. The terms, in order of decreasing size, are boulder (> 256 mm), cobble (256-64 mm), pebble (64-2 mm), sand (2-1/16 mm), silt (1/16-1/256 mm), and clay (< 1/256 mm). The modifiers in decreasing size order, are very coarse, coarse, medium, fine, and very fine. For example, sand is sediment that ranges in size from 2 millimeters to 1/16 mm. Very coarse sand ranges from 2 mm to 1 mm; coarse from 1 mm to 1/2 mm; medium from 1/2 mm to 1/4 mm; fine from 1/4 mm to 1/8 mm; and very fine from 1/8 mm to 1/16 mm. Unfortunately, the entire classification is not as consistent as the terminology for sand—not every group includes size modifiers.”
So the sediments, according to the website, are (biggest to smallest) boulder, cobble, pebble, sand silt, and clay. Okay, we know sand, silt and clay, but where did boulder, cobble and pebble come from? Where is gravel? Probably gravel is the same as pebble. I did little more research to clear up this confusion. Here is the definition of gravel related to this topic from http://dictionary.reference.com/browse/gravel: small stones and pebbles, or a mixture of these with sand. So it is small pebbles! And here is the extra knowledge, there are sediments bigger than gravel- boulder and cobble.
Then we did more on sedimentary rocks and metamorphic rocks. Sedimentary rocks we are familiar with, but metamorphic rocks are quite new to us. Metamorphic rocks are formed from Igneous and Sedimentary rocks. These rocks come under contact with intense heat and pressure, and the product is a metamorphic rock. Intense heat? Okay, what temperature exactly? That was the first question that came into my mind. A little research answered that question. The answer lies in http://www.physicalgeography.net/fundamentals/10g.html : 600 to 1200° Celsius for the complete melting of the rock. WOW! Of course it’s cooler than the Mantle, but it is still very hot. It is so hot that it can melt rocks! Can you imagine that? Here is how melted rocks look like, taken from Google:
I guess it was liquid, because it looks like it was dripping before it hardened!
This is the end of our journey with rocks, at least for now. After all those lessons on rocks, the first thing that comes to mind when someone mentions ‘rocks’ is ‘What kind of rock?’ When I see rocks, I try to find out for myself if I can identify what kind of rock that is (I hope that we will eventually learn how to identify rocks lying on the road!). I don’t see them as ordinary things that lie on the ground for no purpose anymore, because rocks are what scientists use to find out about the past. They are things that people wrote on long before paper came out. Rocks are not useless meaningless things. They are objects that are the ground that we are standing on. I guess everything in this world is also like that, put into this world for a purpose.
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