"Lulu, I've got a question! You've told me that rocks are mixtures of minerals and other things that have become attached to each other!! And I believe you!"
"That's good of you, Lou!"
And you've told me about rocks that form as minerals grow and interlock! And about rocks that form as sediment grains become cemented together!"
"I have indeed!"
"And you've classified rocks on the basis of their origin as igneous, sedimentary and metamorphic!"
"I plead guilty!"
"But I have a question!!?!"
"What's that, Lou!?"
"If you hand me a rock, how can I tell how it formed?!!"
"Lou, I've been waiting for you to ask....!"
"I mean, if I see a rock where the grains are locked in place by material deposited between the grains, I know it was sediment that has been turned into rock by cementation! But if I see a rock with grains that all interlock, it could have formed from the cooling of a magma, from the evaporation of a salt lake, or through applying heat and pressure to a rock that already existed previously! How can I tell what went on?!!""
"Neat statement of the problem, Lou!"
"There are four ways to tackle the problem. If one way doesn't work alone, try it in conjunction with one or more of the others!"
  1. Look at the mineralogy of the rock: the minerals that the rock contains.
  2. Look at the 'texture' of the rock: the sizes, shapes and arrangement of the grains.
  3. Look at the 'structure' of the rock: larger scale features, such as layering or discontinuities.
  4. Look at field relationships: the size and shape of the rock body and how it relates to other rock bodies.
"That magic number 'four'! I hope the magic works! If it does...Oi, am I going to be an expert!!

© 2001, David J. Leveson