How would a geologist identify an igneous rock as extrusive?

A.

An extrusive rock is coarse-grained because it cooled slowly beneath the earth’s surface.

B.

An extrusive rock is coarse-grained because it cooled slowly on the earth’s surface.

C.

An extrusive rock is fine-grained because it cooled quickly on the earth’s surface.

D.

An extrusive rock is fine-grained because it cooled quickly beneath the earth’s surface.

Question

How would a geologist identify an igneous rock as extrusive?  
 
 

 
 

  

  A. 
 
An extrusive rock is coarse-grained because it cooled slowly beneath the earth’s surface.
   
   

 
 

  

  B. 
 
An extrusive rock is coarse-grained because it cooled slowly on the earth’s surface.
   
   

 
 

  

  C. 
 
An extrusive rock is fine-grained because it cooled quickly on the earth’s surface.
   
   

 
 

  

  D. 
 
An extrusive rock is fine-grained because it cooled quickly beneath the earth’s surface.

anonymous · Answer

are you still there

tennis5518 · Answer

An Extrusive igneous rock cools very fast on the surface and is created by lava. Since the cooling process is very fast extrusive igneous rocks have very small crystals (fine grained). On the other hand an Intrusive igneous rock cools very slowly beneath the surface and is created by magma.