N

nonconformity

An type of unconformity in which young sedimentary rocks lie on top of older metamorphic or intrusive igneous rocks.

nonsilicate minerals

A mineral without silicon (Si). See silicate minerals.

normal fault

A fault that drops rock on one side of the fault down relative to the other side.

nuee ardente

This is a type of volcanic activity whose name is french, meaning firey cloud. Associated with pyroclastic flows, they are very hot, sometimes glowing clouds of gas and volcanic debris that is forcefully ejected down the sides of a volcano.

normal polarity

A magnetic field produced by the Earth that is the same as exists today.