Why is dark matter difficult to measure? a) because it does not exist in our galaxy. b) because it disappears when it encounters ordinary matter. c) because it creates so much heat it melts any instruments invented so far. d) because it does not emit anything that current technology can detect

B) Because it disappears when it encounters ordinary matter.  

- Dark matter is very difficult to detect because they have almost no interaction with normal matter.

nucleus

would be most reasonable answer tbh

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.