What are the three distinctive types of Rock? Explain in detail the differences.

1. 79

   CloudExplorerposted 13 years ago

   What are the three distinctive types of Rock? Explain in detail the differences.
   
   In earth science most of us have learned this in grade school, if you will challenge yourself to explaining the difference in rock structure, and possibly write a whole hub on it all.
   
   

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2. 83

   Doc Snowposted 13 years ago

   OK.  I'll challenge myself to see what I can resurrect from those long-distant days.
   
   1)  Igneous rock is one type; it originates with volcanic outflows.  It's called 'igneous' because it originates in this 'fiery' manner; etymologically, the word 'igneus' is related to the English word 'ignite', coming from the Latin 'igneus', meaning 'fire.'  Seems to me that a common variety of igneous rock is basalt-- I must admit, though, that I don't have much mental image of what basalt actually looks like, nor of what its properties are.
   
   2)  Sedimentary rock is rock that forms from sediments deposited upon sea-floors which then solidify over time as a result of the pressure from overlying strata.  Such a process is obviously slow, and this line of thought, if I'm not mistaken, was one of the early clues that the Earth must be much older than it was generally considered to be.  (Charles Lyell is the name of a prominent geologist who famously put this idea forth.)  Examples of sedimentary rocks include all sorts of sandstone and mudstone.
   
   3)  Metamorphic rocks have been subducted deep into the crust of the Earth and transformed by the intense heat and pressure there, only to be upthrust to the surface once again.  If I recall correctly there are many, many types of metamorphic rock, but two of the most notable would be marble and granite.
   
   OK, how badly did I screw up?

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   1. 69

      Nose-in-the-Newsposted 11 years agoin reply to this

      Good effort, but see below if you're interested! )

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3. 69

   Nose-in-the-Newsposted 11 years ago

   Very good, Doc Snow, but, as a qualified geologist, I'll point you in the right direction on several areas:
   
   1) Granite is a type of igneous rock and is not metamorphic. There are 2 categories of igneous rock: intrusive and extrusive. Extrusive includes those that, as you said, outflow onto the surface, such as basalts and rhyolites (these are types of lava). Intrusive rocks include those such as granite, diorite, microgranite, dolerite, and many, many more. Granite is a classic example of an intrusive rock. The crystals have cooled slowly due to the crystallisation process happening at a certain depth within the crust (plutonic depths = 50-100km). This is why you can clearly see the crystals on a granite specimen or kitchen worktop. Oh, there is no such thing as 'black granite' by the way, but that's another story!
   
   2) There are different types of metamorphism too (all with varying grades). Here are the main ones:
   Regional = affects larger areas but ranges from low to high temps and pressures
   Thermal or contact = normally occurs adjacent to igneous intrusions (granite pluton!), so will affect a relatively smaller area. Temperature is high, but pressure is LOW.
   Burial = High pressure but low temperature. This type can produce beautiful rocks such as eclogites and blueschists. Usually occurs at subduction zones (when a tectonic slab is subducted underneath another one at a collisional zone)
   Dynamic = high intensity metamorphism that can occur at a meteorite impact. High pressure (but over VERY short period of time) and high temperature (again, over short time span).
   
   Each type produces different suites of metamorphic rocks. The resultant rock is dependant upon the temperature and pressure combination, and also the 'parent' or original rock. I.e.: a limestone will produce a marble if under regional or thermal metamorphism. But a slate will eventually form a schist under regional metamorphism. An eclogite can form from some types of basalt at burial metamorphism zones.

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